Sikorsky S-76: Ask Nick Lappos

[Heliport]

Sikorsky Press Release
In a move that underscores Sikorsky's commitment to the civil marketplace, go-ahead has been has been announced on future product improvements for the S-76.

"The S-76 has represented Sikorsky's entry in the civil marketplace for the last 20 years and has maintained its reputation as the best helicopter in its class through constant improvement," said Tommy Thomason, Sikorsky Vice President of Civil Programs. "In parallel with S-92 certification, Sikorsky is committed to maintaining the technical and operational leadership of the S-76 by bringing in practical and proven technology and innovative support concepts to be fielded with the S-92.

"The strengths of the S-76 have been its unparalleled safety record, balanced performance, reliability, low operating cost and large cabin that excels for so many applications. Our plan is to insert the latest technology available from our other product lines in a way that enhances these strengths and maintains the S-76 as the customers' clear choice for its size class," Thomason said.

Paul Martin, Sikorsky's Vice President of Engineering, pointed to the technologies involved. "With the technology being incorporated on the S-92 and COMANCHE, and on new international offerings of the BLACK HAWK and its derivatives, Sikorsky has demonstrated a portfolio of improvements that can be applied to the S-76. Those chosen are the ones that bring the most value to our customers," he said.

The improvements taking place were selected by analyzing potential changes in the context of how they would most cost effectively satisfy customer requested features. Among the candidate improvements, the following were considered the most attractive and form the basis for the planned program:

Uprated Engine - Certification of the Turbomeca Arriel 2S2 with approximately 6% more power than the current 2S1. Thomason noted that the 2S2's increased power will be used not only for performance enhancement, but to assure the engine remains in service until the TBO limit is reached: "We are working closely with Turbomeca to see that the 2S2 is designed and demonstrated to achieve maximum durability in the S-76," Martin said.
Integrated Cockpit -- The new cockpit will have flat panel liquid crystal displays, digital data bus architecture and rack adaptability to incorporation of optional equipment. The BFG HUMS will be an integral feature of this new design and the Sikorsky Integrated Customer Support System. Differential GPS navigation with automatic approach to hover will be an option.
Quiet Tail Rotor -- This design incorporates an advanced airfoil design with swept tip and flush fastener attachments. It has been tested and flown to demonstrate its performance and acoustic characteristics. The advanced airfoil provides improved aerodynamic efficiency permitting the rotational speed to be slowed to further enhance its acoustics. This feature will be retrofitable to S-76 aircraft currently in service.
Improved Comfort Interior -- Improved cabin comfort is to be achieved by a to-be-selected combination of passive noise suppression, Active Vibration Control (AVC), Active Noise Control (ANC) and a low noise main transmission. AVC has been developed and successfully tested on the S-92 and is directly applicable to the S-76. It consists of vibration sensors, a computer, power amplifier, and shaker assemblies. The basic approach is to create an out-of-phase vibration that cancels the vibration caused by the helicopter dynamic systems. A production design Active Noise Control system will be flown this year for evaluation. The improved low noise transmission would employ advanced COMANCHE gear designs that have proven their noise reduction capability.

The selected product improvements on the S-76 are tentatively planned for certification and introduction in 2004. Trade studies continue for definition of an affordable and retrofittable de-ice system based on the S-92 design.

More than 500 S-76 helicopters have been produced and are in operation worldwide with customers in more than 40 countries.

[neutral99]

"The S-76 has represented Sikorsky’s entry in the civil marketplace for the last 20 years and has maintained its reputation as the best helicopter in its class .........."


Is it still "the best helicopter in its class"?
If so, what makes it the best?
If not, what is?

What other changes would you like to have seen introduced?

[Flight Safety]

My favorite mods are the HUMS and the increased engine power. The one thing I really don't like about the S76 is it's low altitude hover out of ground effect (1800 ft at gross weight, ISA). The S-76 seems to operate at near gross all the time, so this has restricted the helicopter to low altitude operations. Hopefully the Arriel 2S2s will help this.

------------------
Safe flying to you...

[IHL]

Nick you almost need your own forum, here is my question.

Are heated blades an option on the SK76 C+
and if so is Sikorsky doing any engineering into developing a main rotor anti-ice system for older model 76 aircraft.

Thanks IHL.

[collective bias]

I wonder if Nick Lappos would answer a few more queries.....
Nick, it has been a while since I flew the C model. I wonder if you could quickly run through the OEI Bias system and the what is shown on the IIDS regarding hashed and un-hashed boxes and what it all means.
Also, define transient and static droop as it applies to the 76.
Finally, A few years ago I read an article which had a 76 on fixed skids and some other mod's courtesy of the russians. Has this progressed at all?
Greatly appreciate your time and input to these threads Nick, and if anyone else has time to reply :D

[glsmith]

as i understand it, when you are oei, the N1 box will be hashed, if it is not hashed then you must check what N1 you can pull via the placard.

[Nick Lappos]

IHL asked:
Are heated blades an option on the SK76 C+ and if so is Sikorsky doing any engineering into developing a main rotor anti-ice system for older model 76 aircraft.

Nick answered:
Sorry for the long delayed response, I just stumbled acoss your request!
There are plans to de-ice the blades on the S-76 family in the next few years, but I am not directly connected to those who are planning it, so I have no definite timetable. The baldes are all the same, so it should be easy enough to make it universal to all types of S-76, although the details of markets and approval agencies may change that logic.

[Nick Lappos]

Collective Bias asked:
I wonder if you could quickly run through the OEI Bias system and the what is shown on the IIDS regarding hashed and un-hashed boxes and what it all means.
Also, define transient and static droop as it applies to the 76.
Finally, A few years ago I read an article which had a 76 on fixed skids and some other mod's courtesy of the russians. Has this progressed at all?

Nick answered:
The OEI bias on the C lets the pilot need to recall the N1 limit as a constant, regardless of the fact that the N1 limit varies with ambient conditions. On other Turbomeca Ariel equipped helos, the pilot must look up the limit on a chart while flying out after an engine failure (yea, right!) We Sikorsky pilots asked for a simple calculator to fudge the indicator to always read a constant number, so only one number had to be remembered by the pilot, and no chart had to be consulted.

If the bias computer fails, the indicator tells you that the chart must be consulted. I cannot recall which way is hatched.

For all engines, the reduction in Nr/N2/Np with power application is called droop. If the engine takes a bit of time to come to power, and the Nr droops but then recovers, we call that transient droop. For many engines with hydro-mechanical or hydro-pneumatic controls (not FADEC's), the long term Nr may not be a constant, as the combination of N2 setting thru the beeper, the collective bias and the ambient conditions might all work out to a number somewhat off from the nominal setting. Most engines must reduce rpm as power is applied for engine control stability, so the natural engine speed trend with increased power is a down droop, usually about 1/2 to 1% for each 10% power. This is cancelled by the collective bias, or by a computer governor, in most cases. The permanent droop with power is called static droop. FADECs make all this go away, as they allow very sophisticated control techniques to keep the output rpm very constant.

S-76 fixed skids were considered a few years back, but I don't think it went too far, as the market seemed to like where we were with retractable. The weight of the retract mechanism is about 90 pounds, and the fuel saved by the drag reduction actually saves about 100 pounds per full fuel tank!

[ 29 July 2001: Message edited by: Nick Lappos ]

[offshoreigor]

This might be a good topic for Nick.

I was at FSI a couple of months ago and for the first time since I started flying the 76, I was shown a very simple method that can be applied to either a "Rotten Right" or a "Lucky Left" pedal jam/cable failure.

Apparently this procedure is based on Sikorsky Flight test data from the original 76 program, but for some strange reason, it was never incorporated in the RFM.

Basically all you have to do is once you level the A/C and assess the condition, reduce A/S to 80 KIAS and set your Q to 40%. This will provide a wings level, ball centered condition. When setting up for your approach (run on landing) set 60 KIAS and 30% Q, this too provides a ball centered, stabilized descent for approach at about 350 fpm down. After crossing the threshold, set 40 KIAS and 20% Q (results in about 100-150 fpm) ball centered and stable.

If rotten right was the culprit, brief the PNF, on your command after touch down to slowly retard both throttles to maintain center line. Lucky left, I found you could slow to about 30 KIAS and run on NO PROBLEM, however you can still retard the throttles to keep on C/L.

My question to Nick is, why do we have to get this procedure from FSI and why isn't it incorporated in the RFM? Surely that is better than having a different procedure for every condition.

Hope to get some input from those who are interested.

Cheers :eek: OffshoreIgor :eek:

[collective bias]

On the third page of the 'Ultimate Arbitration' thread, Nick mentioned the position of the servos on the 76 were incorrect.
I have had engineers mention this before. As I understand the casting positions on the GB are wrong and some poor bloke had the unenviable job of figuring the linkage assembles in the mixing section to get the Gamma right. Correct?
One good thing about the arbitration thread is all the new terms. ie. gamma.
Never heard that before....
PS. I promise to listen and learn. :D

[collective bias]

Nick,
Message read and understood. I have trouble remembering the Hashed box indication also but I think (?) hashed is biased. At any rate a refresh on the manuals will reinstall that info. Thanks again

[Lu Zuckerman]

To: collective bias

What you say may very well be true. When I posed the question to Nick regarding the positions of the servos I was asking if they were in the same place as the older Sikorsky models, (fore and aft servo at 45-degrees ahead of the longitudinal axis and the lateral servos disposed 90-degrees to either side of the fore and aft servo). He said I was wrong but he didn’t say why. With that answer I contacted the Sikorsky Service Department. I asked them about both the S-76 and the Blackhawk relative to the position of the servos. I was told that the Blackhawk servos do not connect to the swashplate but are mounted in the control run for ballistic tolerance. With that knowledge I amended my initial info request and asked about the positioning of the control linkage on the stationary swash plate asking if they were the same as the older models. I am awaiting their response.

If you remember in one of Nicks' posts he indicated that he did a lot of test flying where they were experimenting with different bellcranks in the mixing unit to get Gamma right. This adds credence to what you heard.

I also asked if when the cyclic was moved forward if only the fore and aft servo moved or, if several servos moved resulting in a vector to compensate for shifting of Gamma.

[ 31 July 2001: Message edited by: Lu Zuckerman ]

[collective bias]

Morning Lu, Have a great day... I am off to bed. Currently 1am,
regards :cool:

[Coriolis]

I'm not going to try to catch up with the Ultimate....I looked at page three and just knew most of it went straight past me, particularly the bits where one guy slags off another (doesn't that just get SOOO tedious??.)
However (comma), when I did the S76A course with the good people of American Airlines in Florida in 1981, the instructor's explanation of the slightly odd servo positions was that Igor's norm of 45deg offset would have produced bulges in the fairings.....since first & foremost this was to be a sexy looking machine the decision was to twiddle the jacks around a tad....result - smoooooth fairing and that nightmare of a mixing unit just to keep your wrist movement parallel with the required A/C direction.
Lacking both the intellect and the desire to prove myself superior to anyone, I humbly pass on this snippet, which even if incorrect, is hopefully less 'in your face ' than some of the aggro we've seen....(on the other hand Igor's 76 has paid a great share of my mortgage over the last 20 years, so for that, thanks.... :o

[Lu Zuckerman]

Based on what I have heard instructors say in both factory and military schools I would say your instructor didn’t know of the engineering screw up mentioned above or he was repeating what he heard when he went through the school.

Here are a few examples.

An instructor was covering the rotor system on the Sikorsky H-37. A student asked what would happen if a blade broke off. These blades weighed around 260 pounds and the centrifugal loading was around 72,000 pounds. The instructor responded that the blades being able to lead and lag would reposition themselves to close up the gap left by the departing blade.

A Bell instructor was conducting an orientation for some Iranian mechanics and he told them that most of their helicopters were Agusta Bell and that they were constructed in Augusta, Georgia.

Having been a technical instructor my best advice is to challenge your instructors and make them dig for the answers. They are not always right and as a result the students don’t always get it right and cause a lot of damage.

I was on a tour of Army bases checking on the students that had passed through my classes at Fort Eustis, Virginia. At Fort Knox I visited an H-34 group and while there I passed through the hanger. A mechanic was getting ready to rig an H-34 and he was connecting his hydraulic power pack to the aux servo system. I cautioned him that it could cause problems and he should connect to the primary system. About that time his sergeant came out and jumped me for telling his mechanic what to do. I told him it would cause problems and by that time a major came out asking what was going on. Both the sergeant and I explained our positions and the Major asked the sergeant if he was sure. He said yes and the mechanic turned on the power. There was lot of screeching and cracking. When the aux servo centered itself it jammed the rigging pins in the servo support casting. The pins were supposed to be Monel but the sergeant made them out of steel so they had to be cut out. I told the Major that he had just bought a Cadillac and I walked away. I don’t know what happened to the sergeant

[tgrendl]

Always good posts,

I would suspect that the settings you describe probably work for many stuck conditions but not all.

And I would worry about the torque sharing system on final. If you slipped a throttle or power lever slighly off from the other torque compensating might make the last bit of your ride pretty interesting.

I'm going to try the idea when next at FSI, thanks for the thread.

At a hover with stuck left have you tried reducingthe rpm?

The ship will initially spin faster left but with the reduction of the lift equation over the t/r blades it then slows down quite a bit. Have done it to a stop before.

fly safe

[Harry Peacock]

I've done much sim work and instruction on Sea Kings around the world and have found that with any stuck position for the tail rotor setting min power speed (70 kts ish) and putting the ball in the middle by raising or lowering the collective will give you a stable wings level and no yaw situation BUT with either climb or descent! In a climb the secret is to use airspeed to change the power requirement in your favour without changing the collective which is balancing tail thrust.

If the a/c is climbing try reducing air speed and/or rotor speed to get a comfortable ROD and run on speed and set that on finals for a constant speed landing. Further reduction of rotor speed may be needed to settle through the ground cushion and to keep straight once on the ground but as run on should be in the region of 20kts or so should not be a problem.

The descent situation is a bit more of a challenge. Min power speed will give you lowest ROD but high ground speed, there may be 10 kts or so that can be reduced without the ROD increasing too much and this may be sufficient if you've got a runway or big field. A slight increase in collective will also improve things but will cause a yaw, counter this with a little wing low aircraft maintains heading but is sideslipping, if a cross wind runway is available a cross wind landing may be tried using the wind effect to counter the sideslip.

These procedures work in the sim across a wide range of stuck yaw settings and give options to try in varying amounts. Always try the approach profile at height giving room for adjustment/recovery if you start to lose it. :confused:

The above is the condensed version of an article I've written for military flight magazines after some useful info from pruners amongst others, any one interested in a copy give me an e-mail address at [[email protected]]
& I'll send one
:D :D

[ 01 August 2001: Message edited by: Harry Peacock ]

[IHL]

This snippet ( thanks for the word coriolis)
is a little off topic but here goes.

The S-76 Flight Safety training manuals show a check valve in the pressure line from the hydraulic pump/s. If there is such a check valve, then why do the main rotor blades spin backwards, if external hydraulic power is applied with-out the rotor brake on? :confused:

[collective bias]

mmm, leaking check valve? :D
Must be driving back through the pumps into the GB. Why??? dunno without schematics to study but I bet it does the pump no good. Perhaps the return system is responsible. :confused:

[Nick Lappos]

Guys,
This is a great thread, with many good thoughts. We don't discuss stuck pedal in the flight manual because it is really pretty rare (can't recall any in any S-76 in 4 million hours), but it makes good training talk because it exercises the brain about anti-torque and stuff.

I must say that practicing it in a Bell is easy because the Bell has no collective-to-yaw mixing, so if the pilot freezes his feet, it flys like a stuck tail rotor system. In a Sikorsky (Sea King and S-76) the collective will automatically retrim the tail rotor with the pedal stuck, so the pilot cannot simulate a stuck tail rotor control system in flight. If you freeze the pedals and fly around working the collective, the aircraft flys very well, because the mechanical mixing is nearly spot on.

Generally, stuck controls are bad things, and a chance to either become a hero or a goat. I have had several, but not in yaw. I believe that they will come at a bad time, and that the pilot must figure out what he must do to get down. Left pedal is generally good, because if slowed down properly, the aircraft can be brought to slower and slower speeds, but care must be taken because if the left pedal setting is near the limit, a reduced collective deceleration might turn into a nightmare as the left yaw goes out farther, and the aircraft could depart and spin.

The closer to full right pedal the failure is, the more the answer looks like an autorotation.

With either, the pilot can practice trimming in a steady heading sideslip, which is more difficult than it seems when the trim ball is somewhere in Kansas. The big problem in flying at such large tail force conditions is that the airspeed system may not indicate at those angles, and if the speed truly drops, the aircraft will spin. Rule of thumb is Nose Left, raise collective, Nose Right drop it.

[ShyTorque]

Nick,

Please may I emphasise that the good advice given in the main thrust of your last post applies ONLY to helicopters with the main rotors turning in the "American" direction i.e. from right to left as the pilot looks out the front.

It is vital for pilots to remember that for aircraft with the "French" main rotor direction i.e. left to right from the pilot's perspective, the OPPOSITE is true with regard to the "lucky" side. "Lucky left / Rotten right only applies to "American" rotor direction of rotation.

I speak as someone who has had spells alternately flying Sikorsky then Aerospatiale / Eurocopter designs for some years (almost every other job!).

For a while I was heavily involved in the RAF Puma Sim project and flew it from the front as well as instructing from the rear of the box, so I have seen how confused some pilots can get during tail rotor malfunctions. I have also since carried out the FSI S-76 sim initial and recurrent courses and similarly the US Army UH-60 Blackhawk sim courses.

From my own experiences, and I've said this before on another recent thread on this forum about tail rotor malfunctions, but I do think it is worth repeating, - the "lucky" side appropriate to any helicopter is the RETREATING BLADE side. All the pilot then has to remember is which side is the retreating blade side - and hopefully he should remember that from the rotor start!

The "lucky" side is the safe side to keep the nose cocked off towards during flight towards a suitable landing area and on the approach. Also it helps to keep any crosswind coming from that same retreating blade side during final approach with a tail rotor control malfunction, if there is a choice of landing direction. Increasing power by raising the collective then brings the nose around to point straight ahead for a landing, by increasing the main rotor torque reaction. Once the nose comes around towards the straight ahead position you have found the power/airspeed combination at which the aircraft should be best to land. If this lies within the normal landing parameters for the aircraft, then the pilot will have an excellent chance of landing without breaking anything.

Two more points: I strongly advocate any pilot suffering a tail rotor malfunction to carry out a "dummy approach" at height if circumstances allow and personally I am not a great fan of messing around with engine controls to control yaw, as this can complicate the issue (I've seen quite a few pilots get it horribly wrong in the sim)although I would agree that it may be the good thing to try if you are on the ground and about to yaw off the edge of the landing area.

Cheers, keep up the good work.

Edited for typos; it's well past my bedtime.

ShyT

[ 02 August 2001: Message edited by: ShyTorque ]

[Arm out the window]

The RAAF had a pretty good way of dealing with stuck pedals that was developed for the Iroquois and adapted for the Squirrel when we got them. The Squirrels had been modded with a twist-grip throttle (not all that satisfactory in some ways) so the technique was easily transferable.

Your point about the possibility of stuffing things up when engine controls are manipulated is a good one, Shy Torque, but with the luxury of practice most people found they could cope with pedals stuck in a wide range of positions.

The basic concept was a 60 kt skid ball analysis for a heads-up, followed by a long, low finals decelerating in 10 kt increments until the aircraft nose was pointing a certain limiting number of degrees off the direction of travel.
Then, depending on which way the yaw was, you would (for an American helicopter):

a) For too much left pedal, keep going to a rotating hover, then reduce Nr in small increments which would initially speed up the rotation, but then slow it down as the tail rotor slowed until you could land, or

b) For too much right pedal, slow down until the nose got to be 20 degrees (I think it was) off the direction of travel, then maintain that speed until you were over your big flat grassy landing area, then quickly chop the throttle and run on to an autorotative landing.
With a bit of forethought, you could also steer a bit with judicious (!) amounts of throttle as you ran along, although this was a bit of a mind-blower for some.

Widens your options a bit, I guess, although to coordinate 2 pilots to do it to cope with lever-type throttles would be pretty tricky, I'd imagine.

[ShyTorque]

Arm,

You are right about the difficulty of co-ordinating two pilots during the mainipulation of engine controls; we also used to operate the Puma single pilot which meant the pilot didn't have enough hands, with the ECLs being in the roof panel!

On many larger aircraft in the civilian role it just isn't practical to go messing about with ECLs for practice. On many it isn't allowed, even with an instructor on board, so it can only be practiced in a simulator which means it doesn't get done on a regular enough basis for crews to be really good at it. Some will no doubt argue this one, but I maintain that if it happens for real then there will be some element of the experimental for most line crews.

Personally I would prefer an area of hard surface because if a run-on landing is required and the aircraft does touch down with some yaw it is is a little more forgiving i.e. there is less chance of a wheel or skid digging in and the aircraft rolling over. Of course in UK our grassy areas are usually very soft and muddy which makes our problem worse!

It is a really good idea to keep on discussing tail rotor problems. In the past they were seldom covered in sufficient detail (well done, Sikorsky and FSI for having more recently put some detailed thought into it and come up with useful advice). Those who have never seen one for real or in a simulator (like myself a few years back) need to have the basic principles in the back of their mind. Also, on a selfish basis I like to keep my own dull brain refreshed because I see it as a very cheap life insurance policy.

Two engines is great but there is still only one tail rotor drive shaft and control system!

ShyT

[Nick Lappos]

The S-76 servos are not in the "correct" place for simple unmixed controls to be used. We have a mixer on the top deck to take roll control (for example) and split it out to the two servos that must tilt the swashplate properly to affect a pure roll.

The servos would have been in the perfect place, but we decided to put in 17 degrees of delta 3 in the rotorhead after we had designed the main gearbox casting. To redesign the casting would have delayed the program (the boxes were already being poured) so we just fixed the angle with the mixer on the upper deck.

It is interesting to hear all the reasons given here, from all the sources. This explains why Lu is so often misdirected. For many esoteric pieces of aerodynamic and programatic trivia, the answers are not found by calling someone at the "factory" or elsewhere!

[collective bias]

Thanks Nick.

[collective bias]

I also remember the article about the american 76 driver who after having landed safely had difficulty steering through biased braking on the pedals.
He complained that the FM directions were irrelevant to the actual event. I think (and I would've) he closed the throttles to bring the aircraft to a halt.

[Nick Lappos]

Zimmerframe and Collective Bias,

I recall one yaw control problem like this in the long ago past on S-76's (maybe 1980), but it was an oddball, not a typical stuck control/cable/pedal type situation. The tail servo wore a notch in itself after a long time, and the servo just sort of locked itself in the cruise tail pitch position. The pilot (Gulf of Mexico) and I spoke the afternoon of the occurrance. He did a great job of flying home and made a very high speed running landing (about 80 knots as I recall. It might have been possible for him to slow down to the other side of the power required curve and get to 40 knots or so if he had done a near autorotation, but never argue with success! When he bottomed collective on landing, the turn was a mighty one, and he had to chop throttles and stand on one brake to stop the machine. We modified the servo to prevent any recurrence.

Some observations on all this:
1) He really never figured out that it was a yaw problem, because with the yaw/collective mixing as he pressed hard on the pedals, he stopped the collective from going full down. He wasn't sure, but thought he had a stuck collective!

2) When he made his approach, he did what good pilots always do, he sized up what he could do, and made it all come together near the ground. He touched down with no yaw, but at high speed.

3) When he and I spoke, he was not fully convinced that it was a tail servo problem, but they checked the servo and confirmed the guess.

4) The next morning, he told me that his leg really hurt from all the pushing he was doing all the way home, done inadvertantly and instinctively, based on thousands of hours of automatic pedal motions!

I know of no other stuck control problems on the 76 family. Does this one sound like the one you were referring to?

A comment on simulator training - most training sims are not to be believed if you leave the normal flight envelope. Several sims I have flown are quite benign in emergencies that might very well be eye watering. They are excellent procedural guides, but not tools to polish technique or study the effects of large, improbable failures.

[offshoreigor]

Great replies!

Before we digress into an unrelated topic I should mention now that I left out the troubleshooting portion because I was trying to get a feel for what other operators do in their procedures.

I think I should add a little background. WRT the mixing unit in the 76 as it pertains to Collective to Yaw coupling, we all know that in a dead foot or jammed pedal situation, if you were to apply full Right pedal input, the collective would rise, conversly if you were to apply full left pedal, the collective would drop, (maybe).

This known reaction can be applied in the troubleshooting phase as pertains to determining whether you have a jam or a control cable failure. Remember, there are no 76's left without a self-centering device!

Now wrt the comment about manipulating the throttles, first I want to reiterate that we tried every combination of jam/cable/mixing unit failure and the results were the same, without exception.

In a well coordinated crew, the most important factor is to pre-brief the actions to be taken in handling an emergency. I wasn't suggesting that the PNF simply retard the throttles, but that the PF call for "reduce throttles gently Now" followed by "STOP" as the situation demands.

The 76 Crew that went off the runway actually helped in the post accident analysis that developed this procedure.

Keep the posts coming, it's always great to read your ideas and thoughts.

Cheers :eek: OffshoreIgor :eek:

[tgrendl]

Good thread !

Three comments;

1. Depending on landing site, area, gross weight, DA etc I might consider leaving one engine at idle to lock torque compensating out. (right stuck,US type)

2. I had the good fortune to train with an ex vietnam, ex air america pilot (the real company)in the early 80s on stuck pedals. We did hours of them to paved runway and sod. While holding the collective (twist throttle) if you point your index finger down and keep it there it gives you an easy visual reference for which way the nose will turn as you monkey with the throttle.(US type)

3. Landing downwind is not good. At all.

Fly safe

[pitchlink]

Nick Lappos, I seem to recall that Scotia had an incident in the recent past regarding a tail rotor control failure in a 76C. Can't remember the exact details, I will have to look them up, but the aircraft landed safely at Lossiemouth without incident.

[ShyTorque]

Zimmer,

What Nick refers to is known as "off model" responses. This is what happens if the simulator programme does not include sufficient (or incorrect) data to accurately represent what happens for real and it is a well-known issue.

A simulator is, after all, a big boys sophisticated computer game built for a particular purpose. The sim "aircraft" does not actually have the properties of a real aircraft unless those properties are accurately included in the programming. I can assure you that the simulator company does not go out in a real aircraft and fail the tail rotor in order to gain data (obvious really, innit).

Therefore, what is programmed in is a representation of what is assumed to happen. Yaw rates and other effects following on from those rates may have to be mathematically derived and are a "best guess".

A few years ago, I worked alongside a simulator software guru who worked on site at a simulator we were using, as a major customer. He had written the programme into the simulator software. We had some particular problems because it was a new setup and we were using the sim for critical failures that no one had tried much before. The simulator response was definitely different to what the real aircraft did. On a number of occasions I explained the differences and stood next to him as he plugged in his keyboard, typed in raw machine code to change the programme and he had modified the response of the aircraft just like that.

Just bear in mind that a simulator is great for procedures and working out techniques but it may not always be completely representative of the actual aircraft in its response. For example, the helicopter simulator I instructed on would fly a full fixed-wing aerobatics sequence, including inverted flight and slow and four-point rolls! I used to demo it for fun and a few pilots came out both shaken and stirred. I always warned everyone that under NO circumstances should the manoeuvres be tried in the real aircraft because they probably wouldn't have got through the first manoeuvre in one piece.

However, simulators are still the best medium we have for training for unusual emergencies but these possible limitations of the system must always be borne in mind.

A "flying by numbers" approach to any particular scenario in a particular simulator may or may not be 100% valid. I have seen that using two different manufacturer's simulators of the same aircraft type may give slightly different ideas of how best to cope with any one scenario in detail!

ShyT

[Nick Lappos]

Pitchlink says:
Nick Lappos, I seem to recall that Scotia had an incident in the recent past regarding a tail rotor control failure in a 76C. Can't remember the exact details, I will have to look them up, but the aircraft landed safely at Lossiemouth without incident.

Nick sez:
I am not sure, but I think that was a pedal trim actuator/damper failure, which gave problems to the crew (did it tend to run away in one direction?) The crew handled it well, and all was fine, I believe. It did not require the techniques we are discussing here, I think, but I will defer to someone who is more familiar with the event.

Regarding Zimmerframe's point about simulators, I fully agree with you in their value. My only point is that sims are often only half right, and not particularly representative when improbable failures are being practiced. I do agree that as long as the training is reasonable preparation, they are quite valuable anyway.

Regarding the necessity for two crewmen in a given aircraft, the need to manipulate throttles in a very remotely probable event does not justify the second person, in my opinion. If this were true, we would be spending thousands of dollars a year "just in case" when that cash might be well spent preventing more common occurrences. If one looks at helicopter accident statistics, you can see what drives our game, and it is an eye opener. The mishaps are almost always operational in nature (about 2/3 to 3/4). By operational, I mean what are sometimes called "pilot error" (a term I use with great care) accidents. Without extending the thread way off base, I feel that much of what happens to cause accidents is related to the whole operational scenario, from training and equippage, to weather, procedures, displays and the like, usually (and perhaps improperly) all lumped into "pilot error".

I think we all need to work on fixing what actually happens to cause mishaps, and not sweat to much what might happen in the "extremely remote" probabilities, such as tail rotor failures.

I was the program manager on the joint Honeywell/Sikorsky/FAA program which certified the EGPWS system that is now available on the S-76. This might help reduce CFIT accidents to a memory, and this would cut about 30% of all helo accidents.

Here is a web site that has a great PDF file report on helo accidents offshore, based on 1400 aircraft, 1.4 million hours and 2 years. I believe the data is quite representative of helo operations anywhere, even military:
http://www.ogp.org.uk/pubs/300.pdf

Great stuff, and fodder for a bunch of comments from PPRUNERs.

[helmet fire]

Great thread.

Nick makes some great points. I fully agree with his comments about simulators. They are fantastic for procedural training but, like all things, rubbish in equals rubbish out. In other words, the representative ability of the sim is dependant upon the quality of programming. My understanding (Nick will be able to help here) is that an actual aircraft is extensively fitted out with accelerometers, control position indicators, and other data sensors and taken through its paces. The data thus collected is used for the sim program. Accordingly, the quality (like everything else) is dependent upon the budget of the data-gathering phase. Unusual flight conditions are programmed by mathematical extension of collected data and supposition. Therefore, you cannot really "prove" specific reactions to emergencies in the simulator, but the simulation will provide preparation. Nick said something in his article on testing the S92 that is applicable: when faced with actual observed data disagreeing with computed prediction of behavior, the observed data always wins. Also, the lack of vestibular stimulation generated in simulators make them ideal for IFR/Night, Airline type flying (gentle attitude changes and turn rates) and less applicable for low flying, turn and burn stuff, such as autos, tail problems etc, where the pilot includes vetibular clues in his/her effort to control the aircraft.

In response to Arm out the window's excellent post, I would like to add that the practice of bleeding off tail rotor RPM for excessive power pedal problems is, as you say, extremely effective for the UH-1H. However, I have found it to be far less effective on types that actually have a tail rotor that works! For example, in the UH 60 you have to bleed main rotor right off before you see a good reaction (to the point that generators may trip off line). In the B212 (and I presume the B205A1 and maybe the B412), the tail rotor is so effective (at low DAs)that with a decent left pedal stuck forward case, you are unlikely to bleed enough RPM off to help your tail problem before you lose so much main rotor RPM that you risk losing control. This is more so in the IFR B212 that has a form of collective to yaw coupling non-existent in the VFR version.

Forgive me being slightly off the thread topic of the S76.

[ 05 August 2001: Message edited by: helmet fire ]

[John Eacott]

Back in the very early 80's when I was with Okanagan, we had a fatal S76 accident off Thailand (IIRC), which led to the development and installation of the mousetrap to centre the t/r following a cable failure. I'm well out of currency on type, is this mod. still around, and what (if any) effect would it have on the circumstances under discussion?

[IHL]

John Eacott:The "bear trap "or tail rotor centreing spring, sets a negative 2 degree setting for the tail-rotor blades in the event of a double cable failure, allowing balanced flight at 135 and 40 knots . So one could do a run on landing at 40 with no or few problems.

[Harry Peacock]

Concur Nick and Helmets comments on the fidelity of simulators V aircraft and the some times very poor first simulations of some types. In my limited experience caused by commercial pressures of one manufacturer not wanting to give accurate flight data to another. I know of test pilots going straight from the aircraft to the sim to 'fine tune' the sim responses.
BUT having used them for years and instructed in them for too many they do have a very valid use particularly with regards to the big mind bu$$£*!^$ faults such as Tail rotor snags. If you don't try it in the sim and experience 'best guess' symptoms your first try will be when it happens for real :(

Helmet.. Having spoken to pilots, read reports on tail rotor failures and experienced loss of t/r effectiveness in a Gazelle (Fenestron stall......Oh hush my mouth!!) the rates of yaw experienced (150deg/sec+) would not be duplicated by any serviceable sim. More to the point would not be properly processed by the human vestibular apparatus except as a drastic disorientation where the visual apparatus would be required to try to make sense of the world.

And another comment.... To my understanding the drooping of rotor speed is going to have very little effect on tail rotor thrust if stuck BUT (Again) reducing main rotor speed will reduce total rotor thrust! to maintain the flight path the collective will need to be raised to maintain lift. If collective is increased rotor drag increases and requires more torque to maintain the same flight path thus 'using up' some of the excessive tail rotor thrust. :confused:

Right that's it for the mo. Time to give some poor stude a beasting in the Sim!! :D :D
(Most of my victims have actually appreciated a couple of hours playing with different Tail Rotor faults.....or so they said at the time!!) ;)

[Nick Lappos]

Main rotor rpm nudges can be effective at the tail end of a procedure, if the aircraft is almost lines up and just a tweek is needed to get the machine aligned with its direction of travel (a very good idea, skids or wheels, since a roll over can be noisy, expensive and painful).

(All directions are consistent with American and British rotor direction, front blades going to the left)
The rpm is a double whammy, increasing the rpm will act like a boost of left pedal and decreasing the rpm will act like right pedal.

Here is why. If the main rotor thrust is held constant as rpm is changed (for example, collective is lowered slightly with up rpm), then a raise in rpm will lower the main rotor torque exactly as the percent rpm increase. This is because the power needed by the rotor is almost constant, and the power is the torque times the rpm. More rpm means that less torque is needed for constant power. An rpm increase makes the current tail rotor pitch setting (which is stuck) produce somewhat more anti-torque, which produces a left nose movement. Also, the rpm increase will further increase the tail rotor thrust for even more left pedal equivilent.

If the main rotor rpm is reduced, the main torque will increase, requiring more anti-torque, and absorbing some of the anti-torque the fixed-pitch tail rotor is putting out. This will cause a right nose swing. As above, the rpm change changes the tail thrust, reducing it in this case and making the right swing even more pronounced.

The tail rotor thrust changes by the square of the rpm change, and the main torque changes linearly.

[Harry Peacock]

As I understand it increasing rotor speed to increase tail rotor thrust for a low power problem (Low power balances stuck tail) will only have a limited benefit. Too much increase in rotor speed will exponentially increase rotor drag for the lift gained requiring more torque to keep rotor speed....but you are trying to keep torque down so a small + but too much and you'll be into the -'s.

Using a little more power and opposite cyclic to counter the yaw and using a cross wind to counter the resultant drift may get a reasonable run on speed and ROD if not I'd go for an engine off (My auto's are probably survivable)
:)

ps. The Sea King has had several snapped and jammed cables as well as a drive failure or two

[tgrendl]

I think another way to say what Nick stated is so;

,

Imagine the aircraft at a five foot hover with a stuck left pedal.

While maintaining that height above the ground the mainrotor is developing a value of torque. Call it 30.

If you lower the rotor rpm (say 5 percent) and want to maintain that five feet you must increase the collective.

So you've increased the pitch in the main rotor blades (brought the torque value back to 30)and left the tailrotor blade pitch at it's smaller setting and happily, travelling slower.

The lift equation has as it's largest factor airspeed. In fact it's airspeed squared.

Same output from mainrotor,

Less output from tailrotor. :)

[Nick Lappos]

Tgrendl,
I like your way of illustrating the issue, so let me try again:

If while hovering at 100% rpm at torque of 80%, your tail rotor becomes stuck at a fixed pitch setting. If you creep the rpm down to 95%, while holding hover height, the torque will rise to about 84% (1.05 x 80), because the power is a constant, and power is torque times rpm (84 torque times 95 rpm = 80 torque times 100 rpm).

Because the torque is now higher (and the tail rotor has less rpm for the stuck pitch position), the tail rotor thrust is insufficient, so the aircraft will rotate to the right.

In the same circumstance, if the pilot sneaks the rpm up to 105% and holds altitude with reduced collective pitch, the torque will go down to about 75%, and the tail rotor will now be producing excess anti-torque, so the aircraft will rotate to the left.

In other words, the rpm can be used as a yaw control if well handled!

The effects are used in the Huey stuck pedal procedure we have all practiced at one time or another, mostly because the bicycle chain tail rotor control on a Huey was more prone to failure at one time. I do not believe this is true any longer, but I defer to those who have more knowledge.

One comment on all this stuff - we tend to focus on the emergencies that we can practice, so I have seen people do 5 of these stuck pedal procedures in one flight, and 5 or ten engine failures for the remainder. If one studies accident statistics, CFIT and the like are more likely to bite us. Why don't we practice not hitting the ground!

[Harry Peacock]

'Cos we have to do it at the end of every flight.........Oh and we all believe it won't happen to us!!

I still suspect that increasing rpm has an exponential increase in required torque (I'm sure there's a 'V squared' in there somewhere)

(Spelling again...Or too much gin .....I was very...very drunk!!!!!!)

[ 07 August 2001: Message edited by: Harry Peacock ]

[Nick Lappos]

Harry peacock said;
I still suspect that increasing rpm has an exponential increase in required torque (I'm sure there's a 'V squared' in there somewhere)

Nick sez:
Your instinct is correct, the thrust increases with the square of the rpm, and the torque varies with the rpm directly (first power)if the collective is lowered to maintain height, or with the square of the rpm if the collective is not moved. A 5% increase in rpm makes a 10% increase in thrust and torque if the collective is not changed.

[helmet fire]

To tie in Nick's comments and the Vsquared perspective, I would suggest that, in the example - excessive power pedal (left pedal in American helos) - the increasing torque requirement from a reduction in RRPM is caused by Vsquared.

As Rotor RPM is bled off, collective is increased to maintain a constant hover height. The reason this has to occur is because of Vsquared in the lift formula:
Lift = Coefficient of lift X 0.5roe X Vsquared X S.
Therefore, as RRPM decreases, Velocity over the blade decreases, and this effects the lift exponentially because V is squared.

As you need to produce the same amount of lift to stay at a constant hover height, the only variable to change is the coeffecient of lift - ie pull more pitch to increase Angle of Attack (AoA) thus uncreasing drag as well, hence requiring more torque. Clear as mud?
As Nick says, the extra torque would require more left pedal, thus helping your situation. But this is not all that helps. As the tail rotor spins at a fixed ratio to the main rotor, but at much greater RPM, a decrease in main rotor RPM will result in a proportionately larger decrease in tail rotor RPM, and hence V over the tail rotor. As V is squared, lots of lift is lost from the tail rotor, and becuase the pitch is fixed, total tail rotor thrust is reduced thus helping you even more. Going back to the UH-1H, the tail rotor is nearly always at it's peak in the hover so any reduction in main rotor RPM really reduces tail rotor thrust quickly, and small main RRPM decreases are very effective in stuck left pedal forward cases. Incidently, this quirk has caused/contributed to many limited power accidents in the UH-1H, and I seem to recall some mention in the FM about it. Can any one recall?

I guess it gets more complex on aircraft equipped with mixing units because the effectiveness of rotor bleeding depends on whether the pedal jam is before or after the mixing unit. I am guessing that is why it is a hard procedure to practice on these aircraft. Nick?

[Nick Lappos]

Helmet Fire,
The reason why the torque rises when the rpm is bled off is actually quite simple:
It is not because the velocity is lower (which it is) because the collective rises to make more alpha for the lower air velocity, and the lift is a constant (as measured by the fact that the aircraft neither accelerates upward nor downward). In actuality, the rotor is almost exactly as efficient at lower rpm as at higher (same lift for same power) in fact, the rotor on most helos gets a tad better at lift for power as the rpm is reduced a small amount.

The simple fact is that the rotor is eating power, not torque, and at lower rpm, more torque is needed to generate the same power.

Torque is how much twisting force the shaft needs, and is measured in foot-pounds (a unit of torque is the twist exerted by a force of 1 pound exerted one foot from the center of the shaft (like a torque wrench). If the shaft is not turning, you can still exert a torque on it, but it takes no power to do so. If you exert a constant torque on the shaft, and it is turning at a constant rpm, you are generating a fixed amount of power. Turn the shaft twice as fast while exerting the same torque, and you are now generating twice the power.

So power is torque (twisting force) times the rpm of the shaft. At a lower rpm, for the same power you must increase the torque. Remember the rotor needs constant power for constant lift across a small rpm band.

Try this out, hover carefully and precisely in low wind and note the exact torque and engine temperature (TGT, T5, T4.5, etc). It is easy to be precise if you just barely bounce a wheel or skid a little to get the hover precision down to an inch or so. Then beep the rpm down by 3 or 4 % and stabilize at the same height. Note the torque, and engine temp again. The torque should be about 3 or 4% higher, but the engine temp should be the same (because the power is the same, although the torque is different!)

On some model helos, the lower rpm actually takes less power than the higher rpm, and you can measure it this way, note that 3.5 degrees C of T5 or T4.5 equals 1% power on most gas turbines.

[helmet fire]

Roger that Nick, thanks. My helmet is now well and truly alight and getting worse! I am currently flying an AS350 so I will not be able to try your experiment safely just yet. I think I remember the Huey was specifically operated at 6600N2 so that when rotor bleed occured you were initially getting an increased effeciency from your rotor system, maxing out at about 6400N2, before getting less efficient. Any Huey drivers to clarify?

Nick, what happens to N1 in the situation you described. I had always thought it must increase in a bleed situation (along with resultant TGT increase) or are you simply refering to beep down rather than bleed due topping with N1, TGT, Fuel flow, etc?

How does the power/torque relationship effect the aircraft when the tail rotor slows? Is there any applicability of the Vsquared situation I was on about before?

[tgrendl]

Helmet,

I think you were spot on in your really well done description above.

I goofed by simplifying too much and using the term "torque value" instead of thrust value compared to torque value.

As we get back to a five foot hover the M/R thrust is the same and the torque is slightly higher then when we started. (thanks nick!)

So that relationship has changed linnearily and at first glance, not in our favor.

But the gains we have made in reducing tailrotor thrust have followed an exponential path thanks to the lift equation as you stated.

So the resultant works in our favor.

Much as this professional interaction,

Thanks everyone !

:D

[tgrendl]

Sorry, goofed fourth line down in above post,

Going to happy nappy now

Night

[IHL]

With the NR less than 100% the OEI VNE on the S76 is limited to the best rate of climb speed. When conducting the appropriate procedure for a low side speed trim failure you can fly at a speed greater than Vbroc with the NR below 100%.

My question is : why the VNE restriction when OEI.
:confused:

[Nick Lappos]

The S-76A uses a slight reduction in rotor rpm to gain single engine climb rate. The 96% Nr is worth about 75 feet per minute climb increase when the engine is temperature limited. The use of 96% rotor in effect creates the need for a new structural envelope, and could even call for a new Vne chart and the whole structural qualification (in addition to the full 100 to 107% rpm envelope already provided). Since the lower rpm is only useful for establishing single engine climbout, we conveniently controlled it by limiting to flight below best rate of climb speed (one can argue that if you can accelerate above Vy you don't need the lower rpm anyway). This way we give a convenient way to have our cake and eat it too.

[IHL]

Thanks Nick:
But,How does that apply to NR below 100% because of a low side speed trim malfunction? To parphrase the flight manual " flight with the N2 below 100% when conducting the appropriate procedure for a speed trim malfunction is approved with-out restriction" or something like that.

Thank-you.

[Nick Lappos]

IHL,
The issue is one of frequency of use. We flew at 96% Nr up to Vne and in various maneuvers to prove that everything was safe, but we didn't want to take the stresses of that speed and Nr as part of the component lives calculations. The failure case when N2 runs down is rare, so we didn't have to assume that below 100% Nr was a typical case. With OEI practice as a common thing, we would have had a tougher time convincing ourselves and the FAA that those occurrences were rare.

I was the Chief S-76 pilot back then, and part of the decisioning. I wrote the emergency procedures section of the manual (along with Dave Wright, who is the current S-76 Chief Pilot).

[Arm out the window]

If someone hasn't said this for a while, thanks for taking the time to share this kind of information, Nick.

It's one thing to talk in the crew room about why we do things a certain way, but to hear the real reasons given by those who were there doing the initial set-ups is fantastic.

Much appreciated.

[Nick Lappos]

Arm Out the Window:

It is fun to share thoughts with folks from all over the world. I get a real sense of what we do when we all communicate. I get every bit as much out of this forum as I hope I can give. It is the real power of the web, I think.

[collective bias]

Amen :)

[IHL]

That explains it perfectly, thanks Nick.
IHL
:)

[ 21 August 2001: Message edited by: IHL ]

[heedm]

It seems to me that limitations of modern helicopters are economically based vice structurally or aerdynamically based. Ie, Vne is a product of what component life customers are willing to accept and how much test flying the company is willing to do.

If this is true, could an operator pay for further test flying and more maintenance to increase a limit?

Matthew.

[Nick Lappos]

heedm,
Almost all certification/qualification decisions are based on economics, one way or another. If a part falls short of expectations, it will be redesigned and retested to meet the original business plan, and if a limit penalizes the operator it will similarly be retested. The operator's needs are a big part of the decision process, so most likely your desire is almost automatically met. Exceptions might be for those who operate in a corner of the envelope (maybe a pure hover lift operation in a non-crane type helo, for example) where the appeal of a re-do might not be very universal.

Your basic premise is right on, Matt. The economics of component life costs and maintenance made the S-92 team decide to design and qualify all components with 30,000 hour minimum lives, and at least 6,000 hour TBO's on the gearboxes.

The cost to recertify most components is eye-watering. It is not too hard to spend 1 million dollars on aeronautical engineering tasks, and I doubt that any individual operator wants to foot that kind of bill. Mostly, customers vote with their purchasing dollars!

[CTD]

Well said Nick, and great postings.

The price the customer will bear is a serious design driver, and can often be the source of frustration for the specialized operator to which you refer. They are forced to make do with something designed for the broadest customer base possible, or to modify their operation to suit the aircraft.

The "Budget priced, 160 Kt, fuel mizer, all weather, on-condition, full mission OEI, zero exposure Cat A, pull stumps out of the side of a hill at 12,000'" aircraft hasn't been worked out yet......unless you guys have one :D

[212man]

One for Nick...

I understand that the Vne on the 76 is imposed for handling reasons rather than structural/aerodynamic ones. Namely, it has a negative pitch trim gradient. I am curious to know what speeds have been reached in testing, and how the handling qualities change at these speeds.

[Joker's Wild]

While we're discussing higher speeds in the 76, I'd like to know if there's any truth to the notion that the 76, if it suffers a dual engine failure in cruise (say 135-145 kts), will roll at such a rate as to be un-recoverable.

As I understand it, this is something passed along by a well respected training facility in south Florida

Nick? :confused:

[Nick Lappos]

212man,
Vne is actually not imposed on any aircraft, it is usually the speed at which we propose to stop testing because any more is unusable. Few machines are qualified at a physical limit due to structural or handling limiting.

The S-76 has Vne at 155 knots mostly because we decided not to spend lots of test time climbing up after we dove to higher speeds. Many helos since then have also qualified that way, I think.

The Vne for the S-76 once set, also set the maximum speed at which we met the Longitudinal Static Stability (LSS) for level flight. We adjusted the pitch bias actuator (a device that reads airspeed and fools the longitudinal stick to build in LSS) to that speed. We needed the actuator (since removed on most models because it was only needed to meet the letter of the requirement, and had little practical value.)

The LSS maneuver in the FAR says to trim level at .9 Vne, then without resetting collective, push to 1.1 Vne and see where the stick trims to hold that new speed. In the old old days, when Vne was 100, the 10 knot push was no problem, and in fact a good measure of how a pilot would work to trim at the new speed. In a fast helo like the S-76, the initial trim was 142 knots, and the push was to 172 knots, and the 30 knot speed increase lead to a screaming dive at about 2800 feet per minute. Some level flight trim check, huh?

At 2800 feet per minute down, the stick trimmed back right where it started, and the flat gradient was deemed unacceptable, so we adjusted the pitch bias actuator to give 1% forward stick there, and called it OK.

I worked with a group of handling qualities professionals a few years back, and we proposed a change to the FARs that is now in the works that basically looks at a 10 knot push and pull around the level flight trim. This seems to work well now.

For Joker's Wild - Regarding the question of very bad behavior in an S-76 in a dual engine cut, I performed most of those back when, and the aircraft handles quite well, about like most modern helos. If you wait too long with the collective up in your armpits, however, the rpm can get low, and things can get busy. I terms of response to engine failure, I believe the S-76 is typical of most modern helos in its rpm decay, but it has exceptionally good control capability at low rpm, and a very wide and forgiving rpm range. I have autorotated it to touchdown at high weight and at high altitude, and I think it is actually quite good, not a 206, but surprisingly easy. The couple of touchdown autos experienced by customer pilots due to fuel starvation and the like have been quite successful, too.

[Joker's Wild]

Thanks Nick

Now, I've not seen this for myself, but I'm told the latest 76 simulator in WP will in fact roll hard immediately following a dual engine failure in cruise (higher speeds).

I'm also told the folks who run the sim are declaring this to be expected behavior. I find that just a little hard to believe. If in fact the 76 behaves the way I think it does with a dual engine failure, then what they're saying in WP is way off the mark. :)

[Steve76]

A friend of mine recently lost an engine past V2 on a 'C' model and reported a vicious cross coupled LH roll(!).
Sounded really uncomfortable on the phone and I've been thinking about it for a month now.
No doubt there is the lag between event and pilot response; but does this sound correct nick?. They would've been at 97%N1 at least.

[Nick Lappos]

For Joker's Wild, I will check with my friends down at flight safety, because this is not only wrong, it is beyond the simulator's capability to accurately simulate, I believe. Thanks for the steer.

For steve76, there is little response to a single engine failure at all. We typically demonstrate hands off single engine cuts to show this. Without the engine gages, it is not easy to tell when the cut occurs. I think you might be getting some pilot bravado from your buddy! Was he knitting his parachute with a silkworm and a sewing machine? ;)

[BIT]

Nick,

Can I ask a little more about the LSS? Without the actuator, is the Apparent LSS positive up to Vne and what about with the actuator? I am particularly interested with regard to the S76B.

Thanks

[Nick Lappos]

Bit,
Most helicopters have marginal or negative LSS in corners of their envelope, the traits are virtually meaningless to pilots, and not detectable unless careful cookbook maneuvers are flown.

The speed stability and trim characteristics of helicopters are created by the rotor, which has excellent speed/stick stability, but can be disturbed by the fuselage and horizontal tail, which react to climbs and descents more than they do to small speed and angle changes. What the regs try to do is measure the cues a pilot gets which tell him that speed has changed. The stick is the last place he looks, especially if the aircraft has "normal" dynamic stability (where the pilot is constantly moving the stick to keep the greasy side down). The most important speed cue is the nose attitude gradient, where the nose goes progressively further down as speed increases. (remember the "60 knot attitude" that the instructor told you about?) With a good attitude/speed gradient, speed is easy to hold, because the pilot just flies back to the right attitude and all is OK. With LSS, the supposition is that the stick position tells the pilot that speed has changed, and that is just not true.

The funny thing is that FAR/JAR dictates LSS based on speed and stick, but never mentions attitude gradient at all. That is because the fixed wing folks who wrote the first CAM 6 and 7 regs were translating requirements from the airplane world, and airplanes have no attitude gradient, just stick gradients.

I could go on here, and you can't nudge me and tell me to stop, so I will just stop.

:)

[BIT]

Nick,

thanks very much for your detailed reply. I have done a tp course and have an appreciation of the theory you have discussed but having monitored your excellent posts (S92 etc)for a while I was really after specifics regarding the S76 which in retrospect I should not really have asked about here - sorry bout that :)

Please keep up the good work

Bit

[Nick Lappos]

Bit,
No sweat, the S-76 has positive LSS across most of its envelope as measured by the dive till it hurts technique, but at aft CG it is slightly negative. The A had a pitch bias actuator to patch up that corner, and after a short while in service, the FAA agreed that the PBA was unnecessary and allowed it to be pulled. When the B came out, we folded the PBA algorithyms into its Sperry autopilot, and that took care of that. If no autopilot was fitted, then a PBA was required. The B is just like the A, but the people on the program at that time decided the PBA was a good thing, so they kept it.

All the while, the UK authorities resisted removing the PBA on all models. I have lost track of how that stands now.

I was the Chief Pilot on the S-76 in the beginning, and I challanged the FAA lead test pilot to allow a double blind flight eval, where the PBA was randomly switched off as he performed careful trimmed airspeed maneuvers. He refused, saying, "I couldn't tell, so why bother?"

So much for the sanctity of stick gradient requirements. I could discuss the fallacy of lat-dir gradients next, but my fingers are getting tired! ;)

[ 07 September 2001: Message edited by: Nick Lappos ]

[IHL]

Jokers Wild: If you have a total AC power failure at 130 knots with the AFCS equipped 76, you will get a sharp roll to the left that will get your attention. :)

[Steve76]

Nick,
Possibly correct with that assumption....
However, it was a well documented failure so maybe I need some more info.
I'll see if I can get some more specs.
:confused:

[ShyTorque]

Jokers Wild,

I heard about the FSI C+ sim problem with roll early this year. I was also told it didn't like quickstops either. However, it flew perfectly normally when I did my course a few months back. I believe it was a programming problem and not a representation of the aircraft.

ShyT

[Nick Lappos]

Steve 76,
Any roll, yaw or pitch would be due to rotor rpm droop, as there is no other mechanism for the disturbance. How low did your friend let the rotor go? The normal tendency at the 0 to 40 knot range for all US/UK helos is to require right and forward stick to keep the aircraft level and accelerating. Rotor droop with the right stick in (its about 1/2 to 1 inch on most helos) will result in a left roll and a pitch up, both slight. If the rotor is kept within about 5% droop or so, the afcs will handle it and the pilot will not need to correct. If the rpm goes down a bunch more, it would be more noticable. I certainly would not call any handling quality of the S-76 in this regime "vicious".

I have seen documented evidence of one case where an operator got the rotor down to very very low numbers, in flight, and flew home. Very very means way below 60% Nr. I am not sure how many helicopters are that kind to their occupants, but I'll bet not many. So take care what you call my baby!! ;)

[offshoreigor]

A question for Nick.

Does the C model drop the AC Gen in an OEI condition like the A++? If so does this have any effect on the SPZ-7600 or is it powered only by the inverters? I know that on all our A++ (AC Gen equipped) you will get that momentary kick when you go OEI as the Gen drops off line.

Cheers, OffshoreIgor :eek:

[Nick Lappos]

Offshoreigor,
IIRC - All the Turbomeca S-76's use the same electrical logic, and all give the same throb when the AC gen is kicked off line and the inverter picks up the load.

[slgrossman]

Nick,

Going back to the original question for a moment -- While you say the Vne on the S-76 is somewhat arbitrary, is there not an aerodynamic reason for the decrease with altitude and temperature? I'm flying an A++ and find with a light load at altitude I have to back the power off a good 10%-15% from the torque setting at max gross weight to stay under the placarded Vne. It seems like there's more to it than merely correcting IAS to TAS.

Thanks,

-Stan-

[baranfin]

60% I cant believe my eyes? was this right after the engine failure or something???? Talk about slow reactions, I was taught that letting rpm drop below 90% is hazardous to my health.

[Nick Lappos]

Hey.Moe,
The Vne is based on the test envelop that we determined based on S-76A power, where Vne was just a bit faster than a fully loaded aircraft would cruise at the old max continious. At light weights, you can easily beat that speed in any model, even the original A. Even so, it really isn't arbitrary (anymore) because it is the limit, based on the flight manual, and also now helps set the component stresses and therefore the lives. The reason it is at those speeds was based on power available, but now is is cast in concrete, and is the basis for a bunch of things, so please observe it properly. Rest assured that an incursion into the red range will not cause any major problem, however.


Barafin,
The 60% is actually much higher than the data we have, but I am reluctant to publish the actual number to preserve the specifics. I am pleasantly surprised at the fact that the S-76 brought its folks home after that! :cool:

[ 17 September 2001: Message edited by: Nick Lappos ]

[spinwing]

Can anybody tell me if Sikorsky had developed official Cat A (Vertical)procedures for the SK76B (as distinct from Cat A Clear Heliport procedures)......Nick L are you out there????? ...cheers :cool:

[Kalif]

Look at Supp 9 for Gp A Vert, Ground Level and Supp 13 for Elevated Heliports.

[Steve76]

Hello Nick and fellow 76 drivers,
With regard to a internal gearbox failure of the #1 engine, N2 input driveshaft and the subsequent channelling of 100% of the turbines power into the tail rotor. Is it not unreasonable to expect that the tail rotor will overspeed to the point that it suffers a catastrophic failure and disintegrates?.
Hmmmm? :(

[Nick Lappos]

Steve76 asks:
Hello Nick and fellow 76 drivers,
With regard to a internal gearbox failure of the #1 engine, N2 input driveshaft and the subsequent channelling of 100% of the turbines power into the tail rotor. Is it not unreasonable to expect that the tail rotor will overspeed to the point that it suffers a catastrophic failure and disintegrates?.


Nick sez:
You are postulating an internal main rotor gearbox failure, I think, where the engine is still connected to the tail rotor, but disconnected from the main rotor bull gear.

Such a failure would leave the engine driving a much smaller load than the big main rotor, so an upspeed might occur, depending on how big the power reduction is (the reduction from normal drive to just the tail rotor.)

In all cases, the engine overspeed protection will catch the drive up speed if it should get out of hand, since the overspeed protection system is designed to shutdown the engine if the engine shaft breaks, which is a very big power reduction, the biggest possible. The tail rotor is quite healthy at speeds up to somewhere over 130% (I have been to 128 in flight during tests - this is done by professionals, do not try this at home!)

Most likely, the failure you describe would create a situation where the engine would speed up for a second or two, then settle down to about 109% or so, and it would be at about 2% torque, spinning happily with almost no load (just driving the tail rotor). The 109% is because unloaded, but with the cruise collective pitch setting, the engine would be trimmed up a bit by the collective bias. The rotor and the #2 engine would be driving the helicopter, and you would be in single engined flight.

The only problem would be if you decided to then shut down the #1 engine, because that would cause the loss of tail thrust.

[rotorque]

This is probably the wrong thread to add this little story into, but it may have some relevence to any one who drives the Robbie.

The topic reminded me of an overspeed situation that a pilot had in the N.T of Oz around 6 years ago.

Early morning, fat dumb and happy on the way to a job. I hear "oh **** " over the company radio. Not the usual frazeology. Several calls made to said pilot, only to hear a garbled chuckle.

The engine on the R22 rotates a set of belts on a sheave set up. The upper sheave is connected to the drive train and houses the free wheel unit. Just forward of the upper sheave there is a flex plate that allows flexing of the drive shaft as the upper sheave moves away from the lower sheave when the belts are tensioned. Forward of this flex plate the drive shaft goes through another flex plate and then into the gear box. Aft of the upper sheave the drive shaft goes rearward to the tail rotor GB etc.

The yoke that attached the short shaft to this aft flex plate broke. The result of this was a very unsubtle scream from the engine as it oversped. The Main Rotor RPM bled off as the fuselage went in all sorts of directions as the pilot inputed corrections for what he perceived was going wrong.

I often think of this story, trying to picture what the reactions would be. Drooping RPM, screaming engine, exaggerated tail rotor response as the engine drive went directly to the tail rotor.

Have a think about it.

P.S He did a text book auto and put it into a clearing the size of a backyard swimming pool surrounded by sand stone rocks 4 metres tall. .......He was our chief pilot after all.

Cheers.

[offshoreigor]

STEVE76:

I would have to agree with Nick. This condition would not lead to a catostrophic failure, although the load to #1 Eng would be decreased, keep in mind there would still be a restricting load (T/R).

Another point to be consider is that this type of failure, as far as I know, has never occurred and is a precautionary carry over from the S61 days when a TTO (Tail Take-Off) failure was a real possibility.

In fact most companies have eliminated the emergency procedure from their SOP's.

Cheers, :eek: OffshoreIgor :eek:

[tech]

Nick; has this occurence ever been documented on the 76 ??

[Steve76]

On the 'A' model C30 engines we drive, the O/S system has been removed due to random failures which generated their own particular emergency.
That was info I should've mentioned in the original thread.
So, that is why I enquired about the O/S to the TR. I expect the engine govenor will control most of the problem with or without the O/S system.
Igor,
I quite agree that the emergency proceedure is a little dated but I was just curious to hear Nicks opinion, as everyone else round here just shrugs and is a little uncertain.
Cheers CB

[The Nr Fairy]

rotorque :

I heard a similar story about an EMS 412 in NSW which suffered a combiner shaft failure - increasing engine RPM, decreasing RRPM, and so on.

The pilot ( Pete Cook ? ) put it down on a ridge. The previous flight had been a night EMS over similar terrain. And I heard that on the sim check he'd done some months ago he'd specifically asked to go through that specific emergency. Luck or what !

[Nick Lappos]

for Steve76:
The procedure is based on an actual failure that occurred about 15 years ago, where the input gear attachment bolts lost torque and the separation that you describe actually occurred. The gear was redesigned, and no repeat failure occurred. The flight crew noted the problem as noise and rumbling, a momentary upspeed of #1 engine, a swing to the left (extra tail thrust) and then back to normal, with very low #1 torque and high #2 torque.
After a bit of discussion, the crew left well enough alone, and flew home without shutting down #1 (what a good pair of guys! If it works, leave it alone!).

When they landed, they noted that the failure, in that the tail rotor was not connected to the main rotor.
We id'd the problem and fixed it asap, of course, and no repeat has occurred. We inspect all boxes on overhaul for signs of lost torque on that gear to see if any recurrence is creeping back, and everything is fine now.

For Nr Fairy
The above is not like a more common failure that NR fairy notes, where the engine shaft going to the transmission can fail, and N2/Np can go up while torque goes down. In that case, you have an engine power loss, but a healthy rotor drive train otherwise. That can be confusing because the engine rpm on the triple tach goes up, but the rotor goes down. The rotor is your closest friend, so it is wise to make it happy first, of course. Crews can get confused when those needles, always stuck together before, start to disagree.

Also, I am surprised that any A's are flogging around with disconnected electric overspeed systems. They were a pain in the early days (1979) but should be healthy now. The normal governor will catch these failures we describe, I think, so it is not essential to the failures on this thread, but the electric overspeed is helpful for internal engine failures where the power section can unbutton from the compressor, the internal engine overspeed can get very high and engine rupture is possible.

[tech]

Nick ; I don't think that there is an "A" model flying that has the electronic overspeed connected. I think they were removed because of a service bulletin or AD.

I think it is removed from Flight Safety's A model simulator as well.

[Nick Lappos]

Tech,
You are right, the system was deactivated in 1992. My bad.

[Steve76]

Thanks Nick for your informative comments.
Interestingly, I just watched an Icing Briefing from FS that you delivered. Very interesting for a guy who has never flown in snow before. Thanks for the tips regarding constant collective/power settings if suspected ice around. I will be certain to implement them if ever silly/unfortunate enough to get iced. :)

[Nick Lappos]

Steve 76,
That tape has gotten around! The trick of watching torque to detect ice is something I noticed in the spray rig at Ottawa. :D

[tech]

Steve 76, for early detection of ice keep an eye on the wiper blades, they're easy to check at night with a flash light. For some reason signs of icing first show up on the wiper blade side closest to the centre post between the windshields.i.e if in the right seat look across at the left wiper blade and vice-a-versa. A part from torque going up airspeed also goes down accompanied by roughness and shaking, at about this time you've got to do something about it i.e. exit the area.

[Nick Lappos]

Tech,
The problem with using the wipers as ice indicators (I especially like the small hose that provides the washer fluid) is that it may not reliably tell when the rotor is experiencing ice. The issue is that the rotor and the airframe are in two different environments aerodynamically, so the rotor might not be experiencing ice when the wipers show some, and vice versa. It has to do with the fact that the blades are doing near Mach 1 while the wiper is poking along at Mach .2.

I have had ice so heavy that I was descending at full power, with no ice on any part of the airframe that I could see, and I have had 1/4 inch of clear ice on the entire nose with absolutely no ice on the rotor.

The only way to tell if rotor ice is around is to watch for a torque rise with fixed collective and fixed nose attitude. Of course, if ice forms on the wipers, that is a good sign that it is time to be somewhere else.

Of small comfort, but true nonetheless, the engines will behave wonderfully in ice that will otherwise reduce performance to nil. The inlets on the various S-76 models are well suited to ice conditions by design and test.

[tech]

Nick you are correct, I use the wipers as a guide and if they are collecting ice I am planning altitude or heading changes to exit the area.

My experience with ice is only operational and from what I've seen it usually starts at the blade root and travels out.I've read somewhere, though I can't recall where that at 375 knots the temperature rise is appx 16 degrees. That would explain why it starts at the root.

From an operational point of view if you're in cloud below 0 degrees C, you're going to be picking up some ice.

In the good old days we use to transit icing areas but know flight in visible moisture below 0 degrees C is VERBOTEN and flying is much easier.

[ 04 November 2001: Message edited by: tech ]

[Nick Lappos]

tech,
You hit the nail on the head, cold + clouds = ice. If you try to get cute, you'll get caught.

I think the tip heating is about 5 degrees C, from what I have been told. Where do you fly?

[tech]

Nick, I fly EMS in North Western Ontario.

[baranfin]

Quick question, If the slower moving parts of the rotor will ice up easier does this include the swashplate? I would think that if you got enough ice on the plate it would severly hamper the controlability of the ship. Any one ever experienced this? If this is a silly question it's the inexperience talking.

[Nick Lappos]

Baranfin,

The mechanicals are pretty much immune, because the ice is much weaker than the forces these parts handle normally, but this must be proven in certification. One concern is the servo input valves, which need only an ounce or two to create big problems.

[ShyTorque]

This is a question aimed primarily at Nick Lappos if he's around. (Thanks in advance for your support Nick)!

Whilst OEI, the Nr lower limit for the C+ is 93% then 100% whilst accelerating up to Vy but 107% above Vy.

Please could you give a definitive answer why this is so? How critical is this (apart from possibly failing a checkride by busting a limit by accelerating 1 knot over Vy)?

Thanks.

[Nick Lappos]

I helped instigate this in the S-76A back in the early days, and we still use it. The OEI climb rate is better at low Nr (the rotor is more efficient at lower speeds), also you extract maximum rotor energy during the critical low speed fly away and finally you can be sure the engine is producing maximum power if you pull against the limiter, so the procedure is written that way. The climb difference at 93% Nr is small, but worth it.

When you achieve Vy, you are able to transition to normal flight, and the lower Nr isn't needed. To prevent the need for a special Vne and chart at an oddball Nr, the procedure asks that you not go above Vy at a low Nr. If we permitted you to fly to a higher speed, we'd have to publish a Vne for it. It is more convenient for all of us to simply remember to get to 107 when above Vy.

In test, we flew the A to 150 knots at 96%Nr at weights up to 10300 lbs, so you will do no great harm to the rotor to slip up above Vy by a few knots. :cool:

[ShyTorque]

Thanks Nick! Just what I needed. :cool:

[Skycop]

A UK registered S-76B has allegedly recently suffered a very badly cracked tail pylon structure, above the horizontal stabiliser.

I have heard that it may be a known weak point. Anyone in the know able to comment?

[ 06 December 2001: Message edited by: Skycop ]

[RoamingCyclic]

Do you know if the Operator is doing the Tail Rotor Pedal/Cyclic Stick Movement Interlock Check During Pre Taxi. This is an old practice that was known to have caused cracking around Station 440 ( Tail Rotor Pylon )

[Steve76]

Interested to hear the answer to the above question.
We perform the Tail Rotor Pedal check on a weekly basis.
Better go check station 440....... :( :D

[Nick Lappos]

I checked with the S-76 Chief Pilot, and he told me this:
Recently, one aircraft had difficulty with the stabilizer attachment bolts loostening up (not holding torque). They tightened them up several times before replacing them. In the interim, the lose stab caused high loads in the local area, which caused the cracks. A service bulletin will be out shortly on this.

This is the first such incident in the several million hours for the S-76 fleet.

[ShyTorque]

As far as I know, the interlock check was not carried out by the operator so that is unlikely to be the cause.

The reason Nick has quoted seems to give the answer.

Is it true that the fitting of the alternative lightweight stabiliser is a possible preventative measure?

[magbreak]

The dutch have had a few problems with the 76 tail cracking. Not sure if it was the same cause, but apparently they have switched the entire fleet to the lighter stabiliser

[Steve76]

A general inquiry to accertain the reasoning for the -34.4 degree C limit on the 76. Currently it is -32 outside and we are expection lower with a -55 degree wind chill at one of our potential destinations. . .How was this limit created and what are the ramifications of flight in temps below it? I understand it to be a limitation for the Gearbox. Is it a starting limitation or a general op's limit and is the wind chill factor considered in this equation?. .Brrrrr! :)

[IHL]

My understanding or mis-understanding of the S76 certification limit of -34.4 is as follows:. .They conducted the cold weather testing during the month of March and the coldest temperatures they could find (-34.4) were in Tuktyatuk where the testing was conducted. As you are aware March is the beginning of the end of winter in Canada and in order to get a lower temperature limit they would have had to wait untill the following year, and because of production deadlines ect.ect . that was not acceptable. . .The company I work for has a cold temperature limit of -32, that is because of a limitation in the allison engine manual which to paraphrase goes something like " The Allison 250 C-30 engine will run satisfatory down to a temperature of -32 while using Jet A or Jet A-1 fuel" to "operate below this temperature the aircraft must be fitted with the agro-tech fuel filter" yada yada yada. . .

Have a look at a long ranger with a C30 engine and you will notice that it has an airframe fuel filter on it, for that specific reason.

To operate the 76 down to its airframe limit of -34.4 you must use Jet B.

About the certification stuff above I'm sure Nick . .can fill us in on the exact particulars, I heard the story from one of the test pilots at Sikorsky in 96.. .p.s.. .Wind chill is not taken into account, wind chill was developped for whimpy people who live in the South to make it sound like it is colder than it really is ,they will say something like "with the wind chill it is -40" while Northerners will say its -40 because that is what the actual temperature is.

[ 28 January 2002: Message edited by: IHL ]</p>

[Lu Zuckerman]

To: IHL

"Wind chill is not taken into account, wind chill was developped for whimpy people who live in the South to make it sound like it is colder than it really is ,they will say something like "with the wind chill it is -40" while Northerners will say its -40 because that is what the actual temperature is".

In actuality the temperature and the wind chill temperature are different. The actual temperature can be –25 degrees F and depending how fast the wind is blowing the wind chill can measure –45 to –60 degrees F (for example). The wind chill temperature is a perceived temperature and reflects the rate of heat dissipation on the persons body. At least that is what I think it is.

[widgeon]

Is the limit on start up temperature or operating ?. Surely once you have started the OAT is not really relevant for the engine and gearboxes . Might have more effect on rotor hub seals and elastomers . If I recall correctly the BK117 had special seals for Low temp ops that were no good at higher temps. We also had to change all the boots as the naugahyde would get brittle at low temps there was a booster fan in the heating ducts as well I think.

[wde]

My two cents....

I have also heard that there may be a Hydraulic system concern in extremely cold temperatures. We don't have any TANIS heaters on our hydraulic systems... Any feedback on that.

As far as the BK is concerned, the limit is something like -45, but you reach a limit of -32 using Jet A. Below -25, we used Jet B to be safe, but had an operational limit of -40 (C and F) <img src="smile.gif" border="0"> but who wants to be out there at -40, I think at these temperatures, it becomes a real to life human factors issue: What if you go down with a precautionary, or if you have a heater malfunction? Most of us are civilian operators who really have no business flying at these extremely low temperatures. OAT affects the A/C but wind chill affects the people!

[Steve76]

Gidday IHL,. .Hows work? Nice dig at the humans who are blessed enough to be born somewhere WARM and HOSPITABLE <img src="tongue.gif" border="0"> . .Looking foward to hearing Nicks reply..... .Say gidday to those worthless aussies for me.. :)

[MightyGem]

Steve, as said above windchill is a perceived temperature felt by people (maybe animals as well???). For inanimate objects ie helicopters -32 is -32 regardless of the windchill factor.

[volpe]

Worthless Eh........Fatboy. <img src="cool.gif" border="0"> <img src="wink.gif" border="0">

[turboshaft]

The -34C operating restriction for the Rolls-Royce Model 250-C30 in the S-76 aircraft is due to the fuel specs. Jet A and JP-8 both have a maximum viscosity rating of 8 centistokes where JP-5 has a maximum viscosity of 8.5 centistokes. By referencing fuel spec ASTM-D-1655, you find that at -32C you reach the 8.0 centistoke level for Jet A and JP-8.

This is where the note in the Model 250-C30 Operations and Maintenance Manual comes from, stating "The engine will operate satisfactorily on JP-5, JP-8, Jet A and Jet A-1 at fuel and outside air temperatures down to -32 degrees C (-25 F)." For JP-5, the maximum viscosity is 8.5 centistokes, which translates to -34 C.

Operation of the –C30 / S-76 at lower temperatures is not limited by the engine – most operators simply follow standard cold weather fuel mixture instructions, such as adding Av-Gas to the jet fuel. JP-4 and Jet B do not have maximum viscosity requirements, and are thus also used by some operators operating in extreme cold weather environments.

Steve76 - Email me if you have any additional Qs.

T/shaft

[Nick Lappos]

I was the Chief S-76 Test Pilot back then and recall the reason for the limit as -34 degrees C. The limit is based on the qualification and demonstration tests done back in the beginning, where we set -34 as a market acceptable number. There is no fundamental difference between the S-76 and other Sikorsky machines regarding cold capability except for that, even though I do see some interesting sidelights in the above posts. The aircraft will not fail to do anything critical if taken to lower temperatures, but you as PIC will not be legal. The fuel reasons for the limit listed in the posts above are not reasons for the original limit, but they quite well could be true, even so. I do know that we took the Jet A down to -34.4, and that the aircraft flight manual limits should override the engine operator's manual, but a quick call to RR customer service should answer the question.. .The limit is both cold soak/start-up and operating, although the start-up is always the worst condition, since most systems warm up as they turn up. Seals are always the issue, transmission, hydraulic and landing gear.

Regarding wind chill, there really is no such thing, be careful not to get caught in "TV weatherman hype." As defined, wind chill is the temperature you have to take still air down to so that you equal the cooling power of the current temperature/wind conditions. It is semi bulls**t, based on exposed flesh, and is of no use for anything else, like if you have clothes on, or if you are out of the full effect of the wind. It is impressive when quoted on the news, however.

If it is -40 degrees, and 50 knots of wind, a thermometer will read -40. If you shelter the thermometer from the wind, it will read -40. If you take the thermometer from a warm house and hang it in the -40 with 50 knots of wind, it will more quickly get to -40 than if there is no wind (that is all wind chill means).

[ 30 January 2002: Message edited by: Nick Lappos ]</p>

[Steve76]

Thanks for the replies .... .Turboshaft: . .There definately is a fuel temp limitation for the jet B but I cannot see why that is a restriction considering that the Bell 212 can operate to -40 on the same fuel.. .Nick: . .Its a shame that they never got to below -34.4 as this is a definate restriction to our operation and we are only at 51 degrees N latitude. It is (as I assumed...) just a legal issue and it's comforting to know, in your opinion, that temps slightly below that limit should not be cause for serious consternation.. .Another problem is the descepancy between the OAT guage and the AWOS or tower temp. Last night while doing a maintenance run the reported OAT at the AWOS was -33 and the a/c was only reporting -28 !!. Every since I watched your icing video I have paid attention to noting any discrepancy between the two and have tried to apply a correction as necessary. . .Volpe: <img src="tongue.gif" border="0"> <img src="wink.gif" border="0"> <img src="tongue.gif" border="0"> <img src="wink.gif" border="0"> <img src="tongue.gif" border="0"> <img src="wink.gif" border="0"> :)

[offshoreigor]

Hey Steve76

I agree with Nick on the reasoning for the -34. Don't forget that the Jet A is limited down to -32 using PRIST.

As for the 212 down to -40, don't forget that the 212 has heated fuel via the Fuel/Oil Heat exchange so once your started, your getting nice warm fuel to the fuel control!

Cheers OffshoreIgor <img src="eek.gif" border="0">

PS. How's London?

[ 01 February 2002: Message edited by: offshoreigor ]</p>

[sling load]

A few of my colleagues and I had discussions with management in the past about the 365, its data only went up to +40c, when asked to fly the aircraft on +40 c days we refused stating the manufacturer had no performance data for above 40c, ie weight limits, etc.

They stated that as soon as you get airborne you are ascending into cooler temperatures, I said, yes, but you have to land sometime, and if its over 40 c and I mush in, im for a row of outhouses. Dauphins don't like the hot temperatures, and my right boot isn't big enough to hold the pedal all day <img src="wink.gif" border="0">

[Flight Safety]

Just fyi...from the NOAA website, their definition of wind chill...

1. What is Wind Chill Temperature?

The wind chill temperature is the temperature that it feels like outside to people and animals. Wind chill is based on the rate of heat loss from exposed skin caused by combined effects of wind and cold. As the wind increases, heat is carried away from the body at an accelerated rate, driving down both the skin temperature and eventually the internal body temperature. Therefore, the wind makes it feel much colder. If the temperature is 0 degrees Fahrenheit and the wind is blowing at 15 mph, the wind chill is -19 degrees Fahrenheit. At this wind chill temperature, exposed skin can freeze in 30 minutes.

Estimated time to frostbite from exposure due to unprotected skin, seems to be the main reason for the existence of the wind chill factor.

[Steve76]

Igor!. .Londons warmer than Moosenee!. .Great to be here. Thanks for your help.. .I didn't know that the 212 has heated fuel, so that explains that.. .Could you send me another email. I have misplaced your address.. [email protected]. .Met any aussies I know lately...?. . :)

[Cyclic Hotline]

When I'm running around naked outside my sauna here, I like to quickly refer to the windchill chart to ensure I do not "overdo" it! <img src="wink.gif" border="0">

From previous experience, I would not recommend a sauna and roll in the snow if there are any female observers in the immediate vicinity - it might be accurately described as a withering experience! <img src="eek.gif" border="0">

Just to ensure that we keep up with the times, always ensure you keep up with the <a href="http://205.156.54.206/om/windchill/index.shtml" target="_blank">new improved windchill!</a> <img src="smile.gif" border="0">

[LAFalot]

Just wondered what the reasoning was behind the 12 second spot turn limitation for the '76? The aircraft would certainly appear capable of a higher rate of turn in the hover whilst still fully controllable, not that one's tried it of course....... And just to dig a little further, should it be taken therefore that if you only turn through 180 degrees then not less than 6 seconds is required, etc,etc? . .If so, perhaps a better wording in the Flight Manual might be along the lines of 'hover turn rate not to exceed 30 degrees per second...'. .Thanks. LAFalot.

[RoamingCyclic]

The Limitation is due to stress on the tail boom.. .Yes you can assume 30 degree per second as the limitation.

[RoamingCyclic]

A couple of strange electrical occurrences on the A++, would appreciate any info or direction on where to start.

1. Running 100% Nr, battery off, #1 DC gen off. .When #1 DC gen turned on, power is removed from #1 DC Pri bus for about 3 seconds (#1 Fuel flow to zero). .This is not the case on #2 and I have never seen this before.. .Possible clues: - Problem with #1 generator contactor (slow switching from #2 gen to #1 gen)?. . - Problem with bus tie contactor (should stay closed for 2 seconds after no generator power - maybe it's open with no warning light?

2. AC gen fails when either engine goes below 65% N1, as per the Flight Manual. However if the snow blankets are on, the AC gen will stay on line. Question is: if the blankets are off when the engine fails, can you turn on the remaining engine snow blanket and restore the AC gen? (Haven't tried this yet)

3. #2 DC gen will intermittently not come on line until N1 is increased above 65% N1. Doesn't make any difference which engine is started first or if the other generator is switched off to "shock" #2 on. Only increasing the N1 will bring it online. When it is working normally (60% of the time), it comes on line as soon as the starter button is released at 40%N1.

4. Aircraft shut down on ramp. Turn on external power.. .When inverter is turned on the pedals move 2" (to the right) quite forcefully. Vertical gyro (ADI) is just jumping around as it gets powered up.. .AFCS is off. Subsequent attempts to duplicate produced less and less pedal movement until after 4 tries produced no pedal movement. This aircraft has a basic Phase 2 AFCS, but a very strange looking pedal damper (no electrical connections, one hydraulic supply line)

Weird ones aye? Thanks in advance!

[IHL]

2. AC gen fails when either engine goes below 65% N1, as per the Flight Manual. However if the snow blankets are on, the AC gen will stay on line. Question is: if the blankets are off when the engine fails, can you turn on the remaining engine snow blanket and restore the AC gen? (Haven't tried this yet)

Rep&gt;; I don't understand why the AC generator drops off line when either engine goes below 65% N1. It's been awhile since I've flown an A+ or ++ but on the A model the snow blankets are powered by the DC generators under normal operations and in the event of a Generator failure both snow blankets are powered By the AC Generator through the monitor bus phase A for #1 engine and phase B for the # 2 engine.

3. #2 DC gen will intermittently not come on line until N1 is increased above 65% N1. Doesn't make any difference which engine is started first or if the other generator is switched off to "shock" #2 on. Only increasing the N1 will bring it online. When it is working normally (60% of the time), it comes on line as soon as the starter button is released at 40%N1.

Rep&gt;; Sounds like the generator voltage outputs need to be " parallelled".

4. Aircraft shut down on ramp. Turn on external power.. .When inverter is turned on the pedals move 2" (to the right) quite forcefully. Vertical gyro (ADI) is just jumping around as it gets powered up.. .AFCS is off. Subsequent attempts to duplicate produced less and less pedal movement until after 4 tries produced no pedal movement.

Rep&gt;; This makes absolutely NO SENSE!. . . .This aircraft has a basic Phase 2 AFCS, but a very strange looking pedal damper (no electrical connections, one hydraulic supply line). .Weird ones aye? Thanks in advance!

Rep&gt;; The phase 2 has only 1 supply line , it is connected to the #2 hydraulic systems return line and not pressure line , the return line only provides operational fluid to the pedal damper to restrict pedal movement, it is not affected by operation of the priority valve. The phase 3 has a pedal damper/ yaw trim actuator and therefore electrical connections, it is affected by operation of the priority valve.. . . .Hope this may be of some assistance.

[ 28 February 2002: Message edited by: IHL ]</p>

[Nick Lappos]

I feel like a Doctor at a cocktail party. take two aspirin and call me in the morning!. .. .Comments in turn:. .. .1) does sound like a slow bus tie contactor.. .. .2) ouch! You have me there, I don't know. IHL has it right, the DC gens are the normal source for the blankets, AC is backup.. .. .3) This sounds like the gen controller does not recognize the voltage from the gen, so it won't let it on line sometimes. If the gen has lower voltage than the one already powering the bus, it will lose the argumant. You can get it on by turning the other off first, then the controller has nothing to compare it with. Could be controller or gen, a quick voltage check of the gen at 50%N1 will tell. Unlike other DC systems, a bus never connects to two generators at the same time.. .. .4) IHL has it exactly right about the damper, it is purely a mechanical device, getting its fluid from the hydraulics. If all SAS switches are off, the SAS shouldn't jump when power is put on, but they will if any switch has stuck in the on position (or failed that way). If so with a yaw switch on, the gyro flopping will tickle the sas servo on the yaw quadrant, and the pedals might jump a bit.

[Nick Lappos]

Have to disagree with Roamingcyclic.. .. .The limits were set by the turns we did for original certification structural substantiation. We took data while turning, and labled the data "12 second turn". I did most of that flying, along with Dave Wright, the current S-76 Chief Pilot. That set the limit. We have since turned at blithering rates without concern, but never submitted the data to the FAA for increase of the limit. The S-76 was used as a demonstrator for LHX maneuverability, and the FANTAIL demonstrator had no tail cone mods necessary to do 90 degree snap turns in 2 seconds at 120 knots.. .. .But the law is clear, you are stuck with the limit.. .. .As a general comment, few helicopter limits are set by the strength of the sheet metal, most are rotor stresses due to maneuvering. This is not true of airplanes, where the loading of the metal tails or wings directly affects the maneuver envelope. That is why most helo pilots think that pulling too much G or yawing too fast will wrinkle the metal. In reality, the rotors will hit limits, and bearings will wear out early, or blades will get wrinkled if you maneuver too fast or too hard. Seldom will the tailboom or fuselage structure be the problem.

[Steve76]

Thanks guys, I just learned something. <img border="0" title="" alt="[Smile]" src="smile.gif" />

[Av8r]

I fly an S76A++.. .Two questions have been bugging me for a while, can’t seem to get an answer I’m comfortable with.. .. .1. Why 107% Nr for all ops?. .. .2. N1 Over speed limitation. A little explanation for those of you who don’t fly the A++. 2 X Arrial 1s1 engines. The engine over speed protection works like this.. .2 X N2 overspeed probes 1 X N1 overspeed probe per engine. (A) If N2 hits 122%, it shuts down the engine and disables the overspeed in the remaining engine.. .(B) If both N2 probes have failed for whatever reason on an engine, the N1 probe takes over. If the N1 is above 82.3%, it shuts down the engine. (!) . .How and who worked that out?. .If I voluntarily shut an engine down for whatever reason, does that disable the over speed on the remaining engine or is there potential for a double engine failure?. .. .Regards. .. .Av8r

[MaxNg]

AV8r. .. .I have no 76 exp but consider this!!. .. .1st case ......drive shaft failure. .. .If you have a driveline failure between the engine and MGB the power turbine will spin to distruction hence N2 overspeed limit at 122% to prevent this. This failure is more likley and hence the need for redundancy ( 2xN2 probes). .. .2nd Case........ .. .possible power turbine failure ie loss of blades on power turbine would reduce the downstream airflow resistance and would result in the compressor overspeeding.. .. .regarding the figure of 82.3% sorry I can't help you there but the limit may not be set by the design of the power turbine but more to do with ancillaries such as starter/Gen etc.. .. .Incomming !!!!!!!!!. . . . <small>[ 22 March 2002, 10:27: Message edited by: MaxNg ]</small>

[Red Wine]

Considering that the ++ is really an "A" model with 1S1 Arriels rather than the RR C30.....with an increased MTOW........... .. .Something has to give to keep the coning angel under control........if the MTOW increases whilst the Nr remains the same.......guess what happens to the coning angle...???. .. .Increase the Nr, whilst increasing the MTOW....and the coning angle remains acceptable [maybe even the same]..... .. .The 2nd question.........let me get the ++ books out.......... .. .The 3rd question........who certified and flew the first A++'s........??. .. .Keep your revs up...!!!!!

[leading edge]

Max Ng,I don't think that a failure between the engine and the MGB could necessarily as the "more likely" failure. Failure of an N2 overspeed sensor (Phonic wheel type I seem to remember)is more likely.. .. .Deadcentre. .. .Point taken on the coning angle but what about the single engine case where you are still allowed to droop the Nr down to 96%? Surely if coning angle was a problem with increasing Gross weight, you wouldn't be allowed to droop any more in the single engine continued take off case.. .. .Also, the TOGW of the A+ and the ++ are the same and the A+ doesn't require 107%NR all the time.. .. .LE

[Steve76]

Righto..... .I was waiting to hear what NIck had to say but here is what I have dredged from the archives. Forgive me if its wrong its been 3 years since flying the C model.. .All the info on the overspeed system is available in the venerable Flight Safety manual. . .. .1. 107% has been addressed on this forum before. To my knowledge it is simply with the retrofit 1S1 the NR needed to be run at 107 rather than retest and all that stuff test pilots do. Ask Nick or go searching around late last year. The aircraft flys really well at 107 due to the reduced pitch angle. Those with the old 'A' commonly increase to 107 for vertical departures and when the blades are not tracking so well, as the reduced pitch reduces the verticals.. .. .2. If I recall correctly, the overspeed system is NOT disabled if one engine is offline. . .. .Many a check pilot will mention that you could consider pulling the O/S CB to prevent a shutdown during OEI. Remember... you didn't hear that from me. <img border="0" title="" alt="[Smile]" src="smile.gif" /> . .. .The reason for 2 probes is to prevent random electrical signals from accidently engaging the OS system ie. magnetic emmissions while flying over high tension power line. The 82.3% N1 limit is extra insurance. . .. .Both probes run at seperate frequencies to avoid this because the entire purpose of the OS is to prevent a condition of excessive turbine RPM launching the blades out of the engine and through the other donk and associated hardware in that area. <img border="0" title="" alt="[Frown]" src="frown.gif" /> Happy thought.... . .. .Additionally on the 1S1 you will see a very heavy steel ring around the turbine area as a practical preventative to this problem. OS may not only be from shaft breaks etc... but also from govenor or FCU runaways.. . <img border="0" title="" alt="[Big Grin]" src="biggrin.gif" />

[Heliport]

I've heard Nick is on vacation in the UK at the moment.. . . . <small>[ 23 March 2002, 10:18: Message edited by: Heliport ]</small>

[paulgibson]

not wanting to digress from the original question but from memory earlier Arriel's also have the turbine retaining ring fitted and I believe it came about after a AS350 in PNG crashed, killing some Chevron Oil employees in the process after the turbine wheels 'exited stage left' and took out a M/R blade....... .. .Didnt endear Squirrel's to Chevron for awhile...

[Xnr]

Nick....as we all know the collective to yaw coupling in the S76 is there to reduce the pilot workload.....but in tail rotor emergencies things can get confusing...

What is the best method of getting back to terra firma with a FULL right pitch setting?

We have tried a few options including autorotation (75 knots) but the nose of the A/C never really aligns itself with the intended landing area and we end up doing an uncomfortable sideways (yawed right) flare.

If we try a high speed run-on we are faced with speeds of 100 knots + and it doesn't look like the result will be too successful.

What do you think?

[Nick Lappos]

Xnr,

The biggest reason why it is hard to practice the classic stuck pitch tail rotor emergencies in a Sikorsky is that there is no way to shut off the yaw to collective linkage. This means that you always will get increased tail thrust when you raise the collective pitch, even when you hold the pedals "stuck".

You actually have to sneak in right pedal as you raise the collective to wash out the coupling, if you are to try to fly as though a failure had stuck the tail rotor at a fixed setting.

The simulator at Flight Safety is pretty effective at these emergencies, and the flight manual procedures work well (I wrote them, actually!).

Have you tried the sim?

As a general statement, practicing the standard tail rotor emergencies is good coordination excercise, and good for general orientation as to the classic pitch-power-antitorque relationships, but the probabilities of having one for real are virtually non-existant.

With a stuck tail rotor pitch setting, you must find the flight speed and main torque that comes closest to satisfying the tail rotor thrust. Remember that an auto trims almost perfectly at zero tail rotor thrust, and an S-76 can fly at 50 knots sideward (lots of right thrust) with full right pedal, so there will be a mismatch in auto. The best way to correct that is to touchdown at lower rpm, which reduces the tail thrust considerably. Arrange it so that in auto just at touchdown, pull down to 90% rotor at touchdown, and the tail thrust will be almost perfect for a full right tail setting. That will happen in a typical touchdown auto, actually. Again try the simulator.

[Xnr]

Thanx for the quick response.

Have been on the sim at flight safety but cant honestly say that I had the opportunity to play with this situation.

The question I had was for a fixed pitch setting or you could say a failure aft of the mixing unit that causes a full right T/R pitch setting.

As you raise the collective there will not be any change in T/R pitch.

Since the T/R has so much authority I agree that the best course of action is to lower the Nr.

Will the A/C come back into trim in an auto at 90% Nr with a full right pitch setting?

Do you recommend executing the auto at 90% Nr to align the A/C with the landing area or come down out of trim (100-105% Nr)hoping that it will align as you raise the collective in the PULL.

Next time on the sim I'll ask to play with a few of these.

Thanx again.

[Nick Lappos]

Xnr,
Are you practicing such failures with full right pedal in the air? If so, each time you raise or lower the collective, you change the tail pitch, because the pedal stops are not the pitch stops in most mid to high collective situations. It is not particularly wise to fly this type of practice, I think, and is not in any training guide that I have seen, nor that Sikorsky has approved. Who's training guide are you using?

If such a stuck full right pitch situation took place, autorotate normally, set rpm at 100 with collective, and as you touchdown, you will be at 90 as you cushion. Don't trim the rpm low on descent, you need the rpm to make a nice touchdown. Touchdown nose up on mains first, any nose angle will be helped by wheel drag.

[Xnr]

Nick

This conversation is a result of a bunch of pilots discussing worst case senarios.

They are not part of any training guide.

I know the chances of it happening are next to nothing.

I asked you mainly because I thought that it might be something you would have played with during certification.

T/R emergencies can get complicated in themselves but add the collective to yaw coupling and the fact that the S76 has a very powerful T/R and the situation worsens.

Thanks for your input ....lets put this one to rest.

Can I ask you one more question.

When the S76 was certified for a Cat A approach ,was there any requirement to zero groundspeed the A/C before touchdown or was a run - on landing acceptable. The flight manual graph is a little vague and the written explanation ends with " Apply brakes as necessary. " We operate in and out of some small helipads (100' x 100' ). Basically I guess the question is," Is the aircraft cetified Cat A to such a landing site?"

Cheers

[donut king]

The '76 can be brought to a stop/ zero airspeed, oei, touchdown.

Years ago our Songklha boys did it to a rig offshore after an engine failed. Mind you, into wind....low gross weight.... excellent pilot....

we do it in training given into wind....low gross weight..... etc.

[Nick Lappos]

Good input, Donut King!

Xnr, The auto thing with a stuck right tail rotor is interesting. I don't know if it would fully trim at 80 knots in auto at 90% Nr but it would be very close. With a flare and some transmission drag moving the nose left, the landing is OK, in my opinion. The normal auto has a 90% touchdown or so, so I think it all works out nicely.

The Cat A landing needs more time than I have right now, because there are several procedures.

[Xnr]

Thanx for the input Donut King...

I realize that with a bit of pilot technique that it can be brought to a stop.....what we do with it and what it is certified for are sometimes 2 different things......

For example I don't see a vertical profile take off procedure in the Sikorsky flight manual but I have done quite a few vertical profiles.

My question was if the aircraft was certified to the stop or was a run-on landing acceptable for the Cat A certification.

[Nick Lappos]

Xnr,
There are about 5 different procedures for the S-76 family, with ground runs and without, all depending on the engine type, gross weight in the WAT curve, and exact procedures for the approach or departure. The basic one in the flight manual is the airport type procedure, where little attempt is made to shorten the landing distance, or the ground roll.

There is also a ground level heliport procedure, with no dip down after the cut on takeoff, and an elevated deck procedure with a dip below the helideck height after CDP. Both of these procedures are virtually zero ground roll on touchdown.

The FAA measures takeoff distance as that distance from the takeoff spot to clear a 35 foot barrier on climbout after an engine failure, and landing distance is that to clear the barrier on landing and then come to a full stop.

With some skill and practice, you can minimize the ground roll of even the airport procedure. You can land an S-76A on one engine at high gross weight, zero wind and roll less than one helo length fairly consistantly. The trick is to carefully control the speed on the way in, get to just above translational lift with almost no descent and at about 10 feet or so, then flare to kill off the speed, and cushion the landing. Practice with light weight, using partial torque to get the feel. Avoid too much nose up (10 degrees max at touchdown), too much rate of descent at touchdown, and too much rotor droop.

[The Sultan]

Xnr

Buy a 412, it out sells and performs the S-76 and does not have this deficiency.

The Sultan:rolleyes:

[Xnr]

Thanx Nick

I am mainly interested in the S76A model as it has the least available OEI power.

So to answer my question, I guess the A model is not certified to the stop but with proper pilot technique this can be accomplished.

Sultan

Perfomance can be measured in numerous ways.

We like the speed, range, and the large unobstructed cabin of the 76.
The customer likes the low lbs./hr fuel burn.

A friend once told me that a 412 was a man's machine but the 76 gets the chicks.

Cheers

[Xnr]

Nick

What is the reason for the 1 min at idle restriction on the Allison/Rolls Royce engine if the aircraft has been shut down for more than 15 min.

I personally abide by this restriction, (I dont feel that big rush to get airborne) but there are a few who don't.

They say if the press. and temps are in the green you are good to go.

The only thing that I have ever heard that remotely makes sense is that this time allows for oil circulation in the engine.

Do you have a buddy at Rolls that can give us a definitive answer once and for all?

Cheers

[Nick Lappos]

Xnr,

Thanks for the swipe at the Sultan, who should be sent to his room, preferably in a 412 so that he is gone longer.

I am reminded of the hurricane evacuation once done in the US Gulf, where the 76's evacuated twice the number of folks as compared to the 412, due to fuel capacity (range) and speed. The 76A carries more than the 412 Cat A at distances over about 100 miles (scarey distances for Bell drivers).

Regarding ground runs, the certification of the procedure is not really the whole issue. The tehnique I describe is acceptable. Also, we do have at least two zero ground run procedures for the 76A, but I'll guess that you don't have them.

Regarding the idle time, I will check on that with Dave Wright, the Chief Project Pilot.

[Servo Jam]

" A friend once told me that a 412 was a man's machine but the 76 gets the chicks."

Well said Xnr. LOL
:D :p

Cheers

[heedm]

Is there something more in the landing criteria than clearing a 35 foot barrier and stopping on the runway? I ask this because I'd think that with OEI you could stop 35' above the runway, just past the barrier, cut your good engine (not recommending this ;) ) and then zero speed auto onto the runway with no roll.

Maybe I'm just way out, and that is not possible at max AUW with normal pilot proficiency. Or maybe there is something more to the Cat A landing criteria?

Anyone?

[donut king]

Understand your question better now!

For me, Cat A. to a stop is only realistic given ideal conditions... into wind, good technique, no obstructions .....etc

As Nick L. stated, the flight manual assumes an airport/ controlled heliport environment.

Just a few thoughts for now!

Cheers!

[Xnr]

" Also, we do have at least two zero ground run procedures for the 76A, but I'll guess that you don't have them. "

Nick could you describe these procedures.

[HeliEng]

A bit of a tech question for you.

S76C, when the number 1 engine is started (on battery) first, and then start the number 2 engine, all is well and everything starts fine.

If the number 2 engine is started first (again on battery) under the normal start prodcedure (generators on), the number 1 engine will not/is reluctent to start.

If you start the number 2 engine first, then deselect the generators, and then start the number 1 engine, it will start perfectly every time.

We cannot find any fault diagnosis charts etc in either the engine or airframe manuals which address this problem.


HELP!!!! :eek: :confused: :eek: :confused: :eek:

[HeliEng]

Nick where are you??????????????????????










"Some days you are the pigeon, some days you are the statue!"

[Nick Lappos]

Helieng,

Sorry for the delay, the server rehost has not hit my home computer yet, just found this at work. I am checking with the S-76 Chief Pilot, Dave Wright for a more definitive answer, but here is my first shot:

I think it is a bad #2 primary contactor that makes a flakey #2 gen connection to the primary bus. All seems fine with battery bus power (as when you flip off the #2 gen). It could also be that the #2 gen is putting out too little power and the drain drags it down. How does #1 start when you run #2 engine up to flight idle, 107%Nr before you start #1?

[HeliEng]

Nick,

I am posting on behalf of a colleague, so I am relaying your replies to him.

He doesn't know how it would perform under those circumstances I am afriad.

Any further information from Captain Wright would be greatly appreciated.





"Some days you are the pigeon, some days you are the statue!"

[Xnr]

Nick

Sorry I have been out of town for a while.

I am really interested in the procedures you have for zero ground speed OEI on the S76A.

Also, have you found out anything regarding the idle time requirement?

Cheers

[pitchlink]

Hi Nick, hope you might have time for the following question.

The S76A series Flight Proceedures manual states that "checkflights.... should be conducted near a landing field, when feasable, and during daylight hours under VFR conditions." Would you consider doing said flights at night/under IFR if not IMC (even multi crew) to be prudent, and within the bounds of interpretation?

Thanks,
Pitchlink

[Nick Lappos]

Pitchlink,

The general rule is that the checkflight determines the airworthiness of the aircraft for normal service, and that some small but measurable risk is incurred. I wrote that procedure, mostly, and didn't want to tie anyone's hands, but on the other hand...........

If you are at night or IMC, there is less chance for a successful precautionary landing.

I know of one fatal where a night maintenance test flight ended in catastrophe, perhaps due to crew distraction and weather.

OTOH, I must have flown off 20 engine changes in Vietnam after midnight to prep for the next morning's missions.

The flight check manual is not law, it is the manufacturer's recommendation.

[Xnr]

Hi Nick

Sorry I have been out of town for a while.

I am really interested in the procedures you have for zero ground speed OEI on the S76A.

Also, have you found out anything regarding the idle time requirement for the Allison/Rolls Royce?

Cheers

[turboshaft]

Xnr,

Nick will hopefully be able to answer your questions, but if not, for the -C30S idle time requirement you're welcome to contact the Rolls-Royce Model 250 Customer Support team via [email protected], or by phone on +1 (317) 230 2720.


Cheers,
T/shaft

[Nick Lappos]

Turboshaft, judging by your home plate, I'll be you are just the guy to answer the question! Did you know Jack Schweibold?

Xnr, I still have no feedback from Dave Wright, who is traveling and out of touch. I will take a swing at it and say that most such limits are associated with uneven temperatures on the rotating parts that might cause slight out of balace, and when the engine is accelerated, they can cause large oscillations and rubs which can damage the shroud tips as the shafts pass through the resonant speeds.

Turboshaft, is that at all correct?

Regarding the procedures, I can dig up the suppliment numbers, but they are the heliport and helideck procedures, where there is Cat A capability from small ground level and elevated decks.

The landbacks are purely vertical, so there is no ground run, for sure!

Sorry for the delay in posting a reply, my computer went on the fritz for a few days, turned out to be bad memory.

[Joker's Wild]

At the risk of sending this thread off in another direction, I would like to ask a question or two about the S76 Flight Check Procedures Manual.

First, should we as pilots consider the FCPM as something we can use at our discretion to ensure system funtionality if we think there is a potential problem, or must we sit idly by until some higher power decrees the Flight Check Procedures Manual be consulted?

Secondly, should the procedures and checks in the FCPM be considered unusual or abnormal and used only under the most controlled circumstances, or are they in fact something much more straight forward, suitable for day to day troubleshooting?

Simple questions perhaps, but able to generate considerable heated debate when all the right things happen in the right order.

[Nick Lappos]

Joker's wild:

Those are good questions! The checks are for use to assure that systems and items are working properly, and should be used whenever the pilot needs to assess proper operation, but they are not normal procedures. Some of the checks involve disabling or shutting down systems. In such cases, it is not at all a bright idea with passengers aboard, or when the flight situation might deem the action unwise (in the pattern at LHR, or IMC over New York, for example).

I believe that the pilot should refrain from Non-Normal procedures with passengers, especially if on a Pt 135 ticket, unless unusual circumstances dictate.

As is typical nobody would say a thing except if something bad occurs, then there will be 1,000 judges to asssess how good a decision it was.

[Xnr]

Nick

Thanks for the reply.......computer problems are the ****z.

I am interested in Cat A approach to a ground level helipad. Dimensions 100' x 100'.

Is there a certified procedure for this type of landing area?

Cheers

[Nick Lappos]

Xnr,
Shoot me an email at my address and I will get you the details.

Nick

[Xnr]

This email is in response to your email to the Model 250
Customer Support
mailbox regarding C30 idle time requirements. Rolls-Royce
requires engines
that have been shut down for more than fifteen minutes to
stabilize at idle
speed for one minute before increasing power. This requirement
allows the
turbine wheels time to thermal normalize thus limiting the
possibility of
rim cracks.

If you have any other questions, please feel free to contact me.

Regards,
Tom Mitchell

Thomas D. Mitchell
Rolls-Royce Corporation
Model 250 Service Engineer

Thanks for the link Turboshaft!!;) :D

[Nigel Osborn]

Hi Nick,
Long time no see! In the 76, if the ship's battery is completely flat because someone left the master switch on for a few days, would it be dangerous to do an external start and allow the generators to recharge the battery. I thought there were enough built in safety features to prevent a thermal runaway, so I was a bit surprised when the company recalled the aircraft which was now 50 miles out to sea and blasted the two pilots for endangering the passengers.:eek:

[Nick Lappos]

Nigel,
There is nothing particularly unsafe about what the crew did, I think. The thermal runaway for a NiCad is not triggered by charging a flat battery, it is usually caused by massive discharge (PPRuners, please jump in and correct me if appropriate. Even if not appropriate!).

It would be good practice to charge the battery with a careful trickle charge, at constant amperage like a battery shop does it, rather than at constant voltage as in most aircraft. There is nothing special about the S-76 this way, it is similar to most helos in this aspect. Black Hawk has a conditioner analyzer circuit for the battery which does a trickle charge technique.

This is something where we can learn from others, too. Ppruners, please pipe up!

Nick

[w_ocker]

dont know about other h60 operators, but in Aus on our S70A-9s we've got rid of all the Nicads and replaced with Sealed Lead Acid Batteries (SLAB), so no more need for conditioner-analyser.

[400 Hertz]

Depends on the condition of the battery (cell imbalance etc), and local OAT. You will probably find that they have had problems on that particular operation with battery maintenance, leading them to err on the side of caution.

My experience is that most pilots treat the aircraft battery like they would a cars battery, a neverending supply of lights and GPS power to read papers by. Only some of them realise that it might only last for less than half an hour, and that is on a good day (no matter what the legislation says).

Hence the reason for the smiling Avionic engineer changing the battery for you.

[coalface]

The problem with the scenario quoted in the original post is not with starting the aircraft with a flat battery, it is with taking off with a flat battery. It takes a while for the battery to recharge and if the aircraft suffered an electrical generation failure in flight, would the battery have sufficient power to supply essential services until landing if it was not fully charged yet? Possibly in VFR conditions but if the aircraft had to return to an instrument approach, one would be slightly embarrassed if the "off" flags started dropping in half way down the ILS.

[RW-1]

I agree with CF, not the charging issue, but perhaps they violated SOP for leaving themselves open to a total failure and no batt backup.

[Thomas coupling]

Learned something there - thank you coalface. I jump started our beasty the other week - no problems, but I monitored the battery amperage (spelling?) tumbling back to normal and it took about 20 minutes to resume normal...have to amend our ops manual now because of this...errm..

[Thomas coupling]

Both my thermal runaways were caused (post investigation) by a breakdown in the cell structure within the battery causing a massive discharge, this was exacerbated by the high OAT at the time.
The first went off like a hand grenade taking some of the lower cockpit area with it! The second contained itself within the confines of the battery compartment.

Interestingly, the helo I fly at the mo' (EC135) has its battery sitting right next to the output shaft from the MGB to the tail rotor (No1 thomas coupling!!!). And there is no battery containment department. :eek:

[Nigel Osborn]

Thanks for all the replies. Just to answer some of the comments. The battery was new and correctly maintained, albeit in order to save weight, the company had fitted a light weight battery which obviously did not have as much grunt as the usual larger one. To lose both generators in a 76 would be highly unlikely in which case you couldn't do an ILZ anyway, especially where we operated as there wasn't one. Conditions were bright blue vmc although quite warm about 35 C. If the battery didn't like the charge rate, and of course the 76 has no ammeter, voltmeter, loadmeter,etc just an amber light ( like a 1930 Austin 7!), then the battery hot system should come into play if things overheat.:rolleyes:

[Nick Lappos]

Nigel,
I stand by my original judgement, FWIW. Thermal runaway is not an issue, and on a vfr day, there is no electricity needed to fly an S-76 safely, (although getting the gear down will call for pulling that little handle by your knee).

However, there is also quite a good reason to get a full charge or a new battery because those pax might deserve it.

No ammeters is done on purpose, cause the GCU's all are self tending. The typical Huey Volt-Ammeter system is great for spending time on the standard checklist, and of little use otherwise. We took all the reasons why you look at an ammeter (pitots for example) and put the caution lights on current sensing relays, so if you ask for the system and power does not go on, you get the caution light. We do sell meters as an option for those who remain unconvinced.

I learned from all the above posts, thanks, guys.

[offshoreigor]

This a question for all you C+ drivers out there. Heres the scenario:

200+ miles to the offshore facility, 34C and a 160 foot deck.

Any advantage other than better OEI performance on the C+ vs the A++?

After a tersery glance at the numbers, I can see only one extra passenger.

Your thoughts please.

Cheers :eek: OffshoreIgor :eek:

[Sarbe]

Does anyone have any idea how loud it is (in decibels) in the cabin of the 76 with standard paneling ?.

I was recently asked this question and can not find any answers.

Cheers

[GLSNightPilot]

I don't routinely carry a decibel meter with me when I'm flying, but I would estimate the noise as <90dB.

[verticalflight]

This may help you:

S76
Heater off - 105.1 dB(A)
Heater on - 106.1 dB(A)

If you need more information e-mail me.

[email protected]

[GLSNightPilot]

Heater off - 105.1 dB(A)
Heater on - 106.1 dB(A)

Is this with the vents open or closed? Side popout vents open or closed? ISTM that the noise is a lot higher with the side vents open, especially if the open side is forward, & the airspeed also makes a difference.

I don't think you can make one number cover all the possibilities.

[Old cynic]

Sarbe

Suggest you call the guys at either Keystone in the US or what was Air Hanson (now Signature, Blackbushe) in the UK. They will have done loads of cabin noise measurement.

[C+]

Question. On the latest/greatest version of the 76C+ why would Sikorsky wire the Standby Art. Horizon (the fancy kind with flt. director bars and stuff) to the number 1 Nav assuming that if everything were going to crap you would probably lose your number 1 Nav?
Should it not be on the number 2 side? Given a dual gen. fail and most everything is switched off or some other fail resulting in the same situation wouldn't it be better to be driven off the bus that will still be giving you some power?

Anybody?

[widgeon]

Hmmm i thought the stdby normally had a battery pack . Is this defined as co -pilot horizon or stand by horizon ?

[C+]

Please read carefully... THIS PARTICULAR KIND OF AH HAS COMMAND BARS as in flight director command bars that must get a NAV SIGNAL from somewhere. So yes there is an emergency battery self just for this AH. Do you think this battery also powers the Nav radio required to supply the signal to the command bars?? I DON'T THINK SO.

Anyone else with an idea?

[USRotor]

Maybe seems stupid, but do you have allready tryed:

- the manufacteur

or

- the maintenance manual

[C+]

I did not expect the manual would help too much and our mechanics had no answer for me. This is our 5th and newest C+ and the first with this type of AH.
Next time I see the Rep. I will query him but I do not run into him that often. Just thought I might get a quick answer through these boards.
I never posted here before and rarely looked but most of my colleagues use this place for info so I thought, what the hey, give it a shot.

[Heliport]

"I never posted here before and rarely looked but most of my colleagues use this place for info so I thought, what the hey, give it a shot."

Welcome to Rotorheads.
Helicopter people from all over the world post questions here.
I don't know the answers to your questions, but there's a good chance others will.

Heliport

[USRotor]

ok, let's se

- maintenance manual/mechanics

imagine that you have a small problem with the system (we are on a scenario), ask what they will do?? 2 optinios, or fix it (and they need manuals and drawing of the system (thats what you need ;) ) or send it to someone that will fix it, right (and that will be the people that maybe will know...)

(mechanics/maintenance "allways know" :) at least is what they said ;) )

- the manufacteur

a little more dificult... normally the guys that sells the heli, or answer the phone, don't know it... but it is allways a way, a mail or a phone call to the tecnhical/publications department can help...


sincerely, i prefer the first one :)

PS: Maybe the last option:with the drawing of the various bus, and using the breakers, try to simulate the condition ...



"children! don't try it at home!!!"

[NigD]

C+

I dont work on helis (so maybe I should just shut up now) but on corporate aircraft the No.1 nav is hooked to the emergency busbar (battery), as is the no.1 comm/stby inst setc.

I believe that the FD V-bars would not be a requirement to work under emergency conditions (double genny failure) anyway and just the attitude (No.1 AHRS/VG), airspeed (No.1 ADC), altitude (No.1 ADC), heading information (No.1 compass) and other essential services required for the 1 hour duration to get you down safely.

Possibly Nick L. can enlighten the reasoning.

Regards

NigD

[almost canadian]

I agree witht the simulation theory,
next time you have 5 minutes to spare on the ground, leave the machine running and start simulating failures, pulling breakers.
If there's FD bars on the AH, there's also warning flags, so just pull breakers untill they pop up.
Try different scenarios as well, 1 gen versus the other, emerg bus on or off etc., I'm sure this way you will figure it out + it will give you a better understanding how your machine is wired.
By the way do you need any extra pilots out there?

[Shawn Coyle]

There is always a danger of using circuit breakers to simulate failures, as pulling the CB on say, an attitude gyro will automatically disconnect the gyro from the display or autopilot, because the 'power to gyro valid' signal says there is no power. This is a lot different from a gyro which is getting power but sending stupid information to the autopilot or display - how do you know it is going to ignore invalid information?
So, be careful pulling circuit breakers - the real failure can be something different!

[Nick Lappos]

The answer is simple:

The main thing to understand is that the ADI-335 meets two different requirements in one instrument. Standby ADI for power failures and standby CDI for display failures in single pilot operations.

The nav function is a way of meeting the backup CDI (nav control/display) requirement for Single pilot IFR. The idea of the CDI is to cover display failures. If the displays on the pilot's side fail or the bus fails the backup CDI will pick up the other (#1) NAV. If the pilot's symbol generator fails he will be able to use the reversionary mode to copy the copilot's displays on his own normal display but will not be able to control the nav through the display controller ....therefore the backup CDI. If you aren't single pilot IFR you don't need either nav on the standby. Baseline prior to a/c 528 doesn't have it.

[NigD2]

Nick

Whats the reasoning behind not having any nav set hooked up to the emergency bus??

Not as essential to do a precision approach in a heli???

NigD

[Avnx EO]

I can't resist chiming in when Nick starts talking avionics.:) But this has actaully been a hot issue on a number of airframes, driven by a lot of tradition (this is the way we've always done this.) The back up CDI has been a vestige for some time. In most modern electronic (EFIS) cockpits it is no longer required - as can be shown by ARP-4761 hazard analysis. (Loss of all "radio" nav and com in IFR typically being "hazardous" while loss of all radio Nav with com remaining being "major") Most modern EFIS designs could support "Hazardous" level for loss of radio nav without a backup CDI. For example, on the S-76 you can recover from a failed symbol generator by selecting reversion (as Nick mentioned), or from a failed display tube by selecting composite. And that's all still all at the pilot's station. The combined probability of both failures is easily better than 10e-6 and likely approaching 10e-7.

It was a different story with an electromechanical HSI with a failure rate of less than 1000 hours. With no ability to recover information on another display at the pilots station, the back-up CDI was essential. However, even with electronic displays and all their reversion and redundnancy, old traditions die hard with our regulatory agencies. For Example, the EFIS-equiped B-430 was initially required to carry two backup CDIs - one for each pilot (so much for single pilot being the driver in that case.) That has since been reduced to one after significant effort.

So why do we still provide a back-up CDI on the standby for electronic cockpits? In some cases - just because it's there. That was pretty much the case for the BA-609 architecture. We didn't need to by hazard or worload analysis, but since the GH-3000 had the capability, and our pilots agreed it didn't add too much clutter, why not. After all, as an engineer, you never walk away from the oportunity to provide extra cabapility when it's free.

Why the connection to NAV-1? I've heard the arguments that this allows the pilot to cross-check NAV1 while he flys NAV2 (with pilot on the right) - but unless you are flying CAT II approaches, this is a rationalization and not really an issue. The real reason is that most aircraft power distributions are designed to protect NAV1 & COM1 because these were traditionally considered the pilot's radios - something from the starch-wing boys. In the 412 for example COM1 is on the emergency bus, NAV1 is on essential, and COM2/NAV2 are on non-essential. And in the 412, you don't lose the essentials unless you select EMERG LOAD (Which you'd only do to get extended 90-minute battery only ops.)

I and several others have attempted schemes to protect the pilot's NAV/COM for helicopters, but with no success. The problem is that we tend to sell VFR versions with only one NAV & COM installed. And it's just too wierd to install the number 2 system first. It confuses the hell out of pilots, and it makes the guys who do Circuit Breaker panels go nuts. So until the day when we call it Pilot/Copilot or Left/Right rather than 1/2, NAV1 will remain the limp-home, last ditch, protected pilot's nav radio.

Sorry, that was probably a bigger brain dump than you were expecting.

[widgeon]

Thanks for the info Erik , One more question on SPIFR aircraft which bus would the autopilot system be powered from ?.

[Avnx EO]

That's also an issue that generates a lot of controversy. It is really a matter of both the inherent aircraft stability and the perceived workload of flying the unaugmented aircraft in IMC. That establishes the hazard level of losing the autopilot function, which then dictates which power bus it gets put on.

Autopilots, themselves, are typically "non-essential" functions for IFR (typical for fixed wings), but for many helicopters, the autopilot system also provides the stability augmentation and attitude hold capability necessary to make the aircraft tame enough for IFR flight. (keeping the dirty side down).

In single pilot IFR, the pilot has to be able to take his attention away from the controls long enough to get an approach plate out or do similar tasks, without looking up to find that the world has inverted on him. Judging the un-augmented aircraft's tendancy to get to an unrecoverable or vertigo-inducing attitude is a very subjective thing, and there is very little guidance material on the subject. (How organized was the pilot before the failure, how far is the aircraft allowed to go with the hands off the controls for how long, etc.) It's really been a judgement call by the test pilot community and certification authorities. For DPIFR (Dual Pilot IFR), if the autopilot fails, its assumed that one pilot can be totally devoted to actively flying the aircraft, and so there are less issues involved.

In most of the twins I'm familiar with, the hazard level of would fall somewhere in the "Major" to "Hazardous" level. And that is why they typically have dual autopilot systems. I've been told the EC-135 has dual system with a third, limited back-up (I'm not sure what that says about the hazard level, since it's beyond what would typically be required for "hazardous", and less than what would qualify for "catastrophic." - or maybe I don't know enough about that system. :confused: )

As far as power goes, I can tell you that on the 412EP (same system as the S-76) that that the pilot's FCC is on the emergency bus. The co-pilot's is on the essential. But that's to preserve SAS and ATT hold capability. The flight director functions and coupled nav are all expendable.

Hope that answers you question.

[Joker's Wild]

Just when I thought I'd seen it all, another surprise.

Here's the deal:

Both Nr needles go to zero and stay there (on the ground by the way). Take a look around and note that both CB's are popped as well, ESS Bus and PRI bus.

What I don't know is how the Nr pickup on the MGB is wired inside. If the pickup is generating one signal only, and that signal is ultimately split between two independent electrical buses to their respective triple tachs, what might cause both CB's to pop?

Cheers

[ShyTorque]

Possibly a short circuit (to earth) in the instrument itself or its wiring?:confused:

[almost canadian]

did you use rotorbrake on shutdown?;)

[Nick Lappos]

the Nr tach is dual powered, with a single coil in the pulse pickup feeding the indicators (another coil, in the pickup but electrically independant, serves the other ship's needs for Nr, such as DCA or FADEC.) Diodes isolate one power source from another.

Sounds like a short in the instrument to me. What did it turn out to be?

[Joker's Wild]

Problem turned out to be the pilot's triple tach.

Should one be surprised that the copilot triple tach went u/s also?

Seems to me I heard a story a long time ago concerning the way the pilot and copilot triple tachs were wired (linked), or something to that effect, although I can no longer remember what the details were. It's been a while so I might be out in space on this one.

Cheers

[Coriolis]

What you need is a 'B' (or a'C'?)

Then you don't need a triple tacho at all 'cos you just know that Nr's gonna be 107 regardless, and P&W's favourite sons are gonna do what it takes to keep it that way while 4 EECs look after them.....now that's class

Shame about the first try with the C30s!

What was all that about the PBA being a no-go item until the 'B' replaced it with a fixed length rod???? ;)

[Xnr]

Nick

After our chat on the phone the other day I found quite interesting your analysis of the capabilities of the S76 wheel brakes.

You stated that if you were concerned about burning up real estate on a rejected OEI take-off or an OEI landing that placing the aircraft on the ground and applying the wheel brakes would out perform the aerodynamic braking ability of a 20 degree nose up flair.

With over 3000+ hrs on the machine I never believed this to be true. I fact I feel that quite a few other S76 drivers are of the same opinion.

I put this out here so you can share this info with our fellow S76 pilots.

Jump in any time.

Cheers

Xnr

p.s. I am researching a Canadian pub for you regarding VRS vs. SWP

[IHL]

Xnr: if you were to touch down at 15 degrees nose UP, there is a great risk of crunching the tail cone. @20 degrees nose up you would most certainly 'DRAG THE TAIL".

[Nigel Osborn]

With most wheeled helicopters and certainly with the 76, the shortest stopping distance is obtained by getting the machine on the ground quickly and applying full brakes. Much above 12 degrees nose up will guarantee a tailboom repair job!:D

[Xnr]

Boys

I didn't mean to confuse you......but with over 3000 hrs on type I think I know that you can't hold that flare below 30' AGL on a S76.

Cheers

Chris

[IHL]

XNR sorry; But one can't assume. I've seen experienced guys do some bizarre things.

[GLSNightPilot]

I have to agree that the ground will slow you more quickly than the air. There just isn't that much friction in the air, & the S76 doesn't like to slow down up there. You might need to replace the brakes & the wheels when you're finished, but that's better than the entire machine.

[IHL]

GLSNightPilot:

My experience has been that on a dry runway the brakes are not powerful enough to lock up the wheels. One maximum performance brake application won't ruin the brakes either.

The only time you risk grinding down a tire is when the runway is wet. Then its easy to lock up the wheels.

[GLSNightPilot]

Perhaps, but we used to have a set of wheels above the door to the pilot's lounge here that were worn through the treads when an unnamed pilot taxied to the fuel pad with the brakes locked. The wheels never even tried to turn, while the pilot was wondering why it took so much power to taxi. I think I'd try to have the brakes locked before I hit the ground, in the above scenario. Fortunately I've never had to try it for real.

[Brother]

IHL

My experience is that the brakes ARE good enough to lock the wheels on a dry runway at max run on speed on 40 knots. If yours are not then you should get them checked.

B

[Nick Lappos]

Comments on breaks and tires and aerodynamic breaking:

Brakes on helos are not exactly like those on cars, but they are powerful. The friction of a tire is large, about 75% of the weight that it supports. For an S76, this means that the two mains can put about 5000 pounds of deceleration on the aircraft, probably about .4 G

The brakes on an S-76 will certainly lock the wheels with full bottom collective, I have left dark black stripes and blue smoke during Cat A and Cat B landings, and the tires made a thumping feel as they rotated after that!
Tires make the most stopping force when they are at 95% of the ground speed, ie just slipping, not stopped. That is how ABS and "pumping the brakes" works. Skidding tires are quite a bit poorer at stopping.

Aerodynamic breaking is a very poor way to slow a helicopter. With normal attitudes, about .1 g is all that is available. Even with ridiculous nose up attitudes, like 20 degrees, the thrust of the main rotor that is actually decelerating you is about 25%, or about .25G, a lot less than the brakes can provide.

If you are on the ground, nose wheel off, mains on, the rotor is even less effective, because it is producing less thrust, and therefore has less decel capability. This situation, (mains on, nose off) is also bad for aft stick on most helos, because of the possibility of making a blade tailcone contact. The 76 has a control limiter to keep this from happening, but many helos do not(including original 76A's that have not had the control system mod - ask maintenance if the limiter SB has been installed!) , and it could be a bit more expensive to replace the blades then to replace the brakes!

[donut king]

Picture this situation XNR.....!

Two 76's side by side...
One on the ground...one in the hover..

15-20 kts forward speed( just an arbitrary number)

wheel taxiing 76 JAMS on the brakes while the hovering one flares 20 degrees.

Which one stops first???


While you're at it...... Two trains leaving at the same time...one travelling east, the other west......!!!!!!!!!!!!!!( just joking!!!)

D.K

[ShyTorque]

Nick,

I tried today to leave some black lines behind the aircraft. Failed completely. Grass and sheep all dead. Where am I going wrong?

;)

[Nick Lappos]

See, ShyTorque, I told you they were powerful........

In the States, dead sheep mean lots of Environmental paperwork, I'd suggest staying off the brakes.;)

[IHL]

Brother & Nick:

I guess my little legs ain't strong enough, cause I anin't never seen them wheels locked up when the collectived was full down.

Of course if the brakes were locked before touch down, well thats a different scenario.

[Xnr]

Nick

I agree the brakes are the most effective way to stop the aircraft.

You also stated that a 20 degree flare is somewhat rediculous. I quote, "Even with ridiculous nose up attitudes, like 20 degrees,..."

It begs the question....For a cat A rejected take off, why does the flight manual call for that flare as opposed to placing the aircraft back on the ground with speed (less than 40 knots)and apply full braking.

Would this not minimize the stopping distance and be safer for passengers as well.

Cheers

[Nick Lappos]

XNR,

Great questions, yet again! Some reasons:
1)The brakes are very effective, but they have energy limits. The max brake application speed is 34 knots
2) On anything but a very smooth surface, speeds above about 15 to 20 knots can be very bad on the gear, and on control while stopping (skidding, etc.)

Nick

[GLSNightPilot]

So let me see if I have this right:

If possible, stop in the air & touch down with little or no forward movement. If you don't have enough room, brake aerodynamically as much as you can, then touch down at or below 34 kts, & brake as hard as necessary. If you don't have enough room for this, touch down as soon as you can & brake as hard as possible, resulting in possible damage to the aircraft, but probably less damage than hitting obstacles with the blades.

Is that pretty much the logic you'd use?

[Xnr]

GLSNightPilot

If over anything but a firm smooth surface (asphalt) the less airspeed the better.

If over a firm smooth surface (asphalt), to do things as short as possible and be within the limitations of the flight manual, I think you hit the nail on the head.

Cheers

[Nick Lappos]

XNR and GLS,
I think you have it right, although I admit I never thought about it all that much. The old NL comment follows, look at the accident statistics, and note how few engine failures there are, let alone those at critical points near takeoff or landing.

Be sure to devote about 100 times more energy on IFR procedures, night off field procedures and CFIT avoidance!

I would also say that if you are going to run into something, be on the ground, so the most you get is a traffic ticket ;-)

[GLSNightPilot]

Be sure to devote about 100 times more energy on IFR procedures, night off field procedures and CFIT avoidance!

Nick, that's pretty much what I do. A single engine failure, even on takeoff, shouldn't kill you, especially from an elevated heliport with water underneath. Flying into the water or other obstacles at cruise speed or with no control just might. That's where most of my energy goes, especially in the dark.

[Nick Lappos]

GLS, that's cool, I fully agree.

My previous post was not ment as a shot, please take no humbrage (what ever that is!). Your attack on the engine failure siuation is exactly right, IMHO.

Nick

[GLSNightPilot]

Nick, I take no umbrage. My pockets aren't big enough to hold much of it. ;)

I think I was agreeing with you.......

[donut king]

Well said Nick!

Couldn't agree any more!

With all the technical stuff we deal with, sometimes we get tunnel vision and forget to PRIORITIZE( sp).

[wde]

The company I work for is currently in a bit of upheaval/transition in its standards department. I am looking for anybody whose companies fly S76A models who may be willing to share SOP's and the Emergency Checklist with me.

I realize that SOP's are sometimes considered trade secrets but in the spirit of this forum, I need to ask. We have a large body of experienced pilots who come from a wide variety of backgrounds. Sometimes, it appears that the amalgamation of SOPs from an offshore op to an EMS op brings with it more turmoil than one might otherwise expect. After all, it is still an S-76!!

Any assistance to this matter would be greatly appreciated...and if you ever make it over to Canada, rewarded with the beverage of your choice. ;)

Thanks

[misterbonkers]

Sounds like you work for the CAA!!!!

ha!

[widgeon]

dya mean Canadian Automobile Association ?.

[misterbonkers]

Civil Aviation Authority (UK)

a.k.a.

Close All Airfields

a.k.a.

Cash And Agro.

Now, i do wish to point out that the above names are only what i've heard, not what I think. I never have any problems phoning any of the departments, the phones are always answered first time round.

:D

However, I do believe that there is a reform going on, and, of late, the CAA seem to be really pushing GOOD things, so keep up the good work!!

[John Eacott]

WDE,

Check your PM's.

Ski season's coming up in your neck of the woods, maybe I'll be by for that beer ;) After we finish with these pesky fires, of course :rolleyes:

[donut king]

Here's one for you Mr. Lappos. ( from us lowly line pilots)

When I read the '76 flight manual cat A or cat B profiles, I attempt to fly my a/c as close as possible to them( given ideal/ favourable conditions...etc...)

When you and your colleagues WRITE those profiles, how intense is the testing? Different weights, temp's, ...etc...?

As I understand flight manuals, they are "legal documents" that a/c manufacturers must have certified along with the a/c.

Anyone's response is much appreciated( just directed to Nick L. as I fly the '76)

D.K

[Nick Lappos]

donut king,

We do take lots of care in making the Cat A takeoff profiles, and the FAA/CAA do lots to check them too.

We determine the performance by trial and error, based on a core procedure that we have simulated. We vary the acceleration, cdp altitude and speed until we get something that works well, is repeatable, and doesn't need excessive skill. Then we test that procedure under varying weights and power levels, and also at the various altitudes that the aircraft is approved for. The testing is fairly extensive, it usually takes several weeks of flight test to get a workable procedure, then a few flights at each check point, and at each extra altitude.

The flight manual areas that describe the operating limits, normal and emergency procedures are all legal documents, and are written, tested and changed with great care.

[Steve76]

Nick,
I understand you are off to Alaska soon for 2 years of winter trials with the S92. True or False?
Seems to me 2 years is a long long time in Alaska :D

[GLSNightPilot]

I have unfortunately been in Alaska several times in the winter, & 2 hours is a long time there, never mind 2 years!! :eek:

[Nick Lappos]

Steve76,

The #3 S-92 will go to Alaska next month for it cold wx certification which will take about 1 month. We have had a good spell in the climatic hangar at Eglin AFB (some unwritten rule of fligh test says that you go to the cold wx chamber in July in Florida!).

GLS is right, time gets kinda slow at -40C!

We also launch the snow tests in #4 in January, which are always interesting. We have to show no problems in snow warmer than -3C, with visibilities below 1/4 mile, which usually means indefinate ceiling below 100 feet. Interesting flying weather. In the 76, we were the only thing flying within 100 miles when we did those tests!

[widgeon]

Hope you have more luck then Eurochopper , 2 years ago they had the EC145 in Alaska for cold weather testing and did not get below zero for about 2 weeks , I think Agusta may have been there at the same time. We took the EC120 to Churchill Man at the same time and had plenty of cold.

[Barannfin]

So Nick, were looking at least a few more months for certification? Or is there more stuff to do after this? Cant wait till the 92s start rollin of the line.

[donut king]

Thank you Nick for your response!

It is exactly what I wanted to hear!!

D.K

[SASless]

Except for being a Teetotaller...I would imagine ol' Nick would be fairly awash in Mr. Jamison's best anti-freeze during his stay in Alaska.

Mind the Snow Snakes, Nick....one should always have a jug handy in case of being bit while doing a one squat. Please to recall the Bush Company and Chilkoot Charlies have a very effective way of warming up the old internal heat level.....and remember to throw your empty goober shells on the floor at Chilkoots or you will be fined a small sum for that minor felony (not throwing them on the floor!). Also...encourage your engineer types to blow the old French Horn at the Birdcage.....on Turnagain Arm....gets them a free drink as I recall!

The Knee Dancing Champion of All Alaska now resides in Fort Worth, Texas.....but he might be willing to offer you some tips for improving on his record.

[Mikila1A]

Nicky baby,

When is the first prod ship suppose to be delivered and to whom.

Did I not read somewhwere that the first couple are going somewhere in Canada to a offshore outfit there.

Cheers

[Nick Lappos]

The S-92 will be FAA Part 29 certified in a few days, scheduled for 20 Dec with virtually everything completed except for the last few component tests, which are running a full speed in the test lab. We have prepared over 1450 FAA approved reports, with less than 25 to go, and we have the final Type Cert Board meeting on 17 Dec. No glitches are expected.

The cert will be the first for Flaw Tolerant structures in helicopters, as well as full bird strike protection and turbine burst protection. All these things complicated the testing, but result in measurable safety enhancement.

Next year we do the cold, high altitude landings, JAA cert, rotor de-ice and snow. First deliveries are in the first quarter of 04, with a Canadian customer for the #1 aircraft.

Sasless,
Since I am the Program Manager (capitols denote a deepening of the voice as we say those words....) I get to decide if I go to Canada in the cold tests, and I think I am needed in West Palm Beach right about then!

[Tiercel]

Nick, Alaska is in the United States, not Canada.

[widgeon]

shhh , don't alert them we are about to annexe it with our formidable armed forces .

[Nick Lappos]

OOPS! Well, after a brain fart, let me recover by saying that the aircraft is going through Canada on its way to AK. Besides, didn't a Canadian invent coldness?

[Mikila1A]

So since it would appear that the Nickmister can not devulge who the first customer will be, maybe some one else may have a inside clue who will be driven the new ships over there.

And what is the address that should be on my CV.
:D

Cheers chaps

[Shawn Coyle]

If I can add my two cents worth to the discussion - the procedures and performance are checked pretty thoroughly by the certification agencies concerned - and not just once. It seems that each new country will want to spot check at least one or two of the Cat A procedures.
We also spend a lot of time going over the wording of the flight manual to make sure it is as idiot proof as possible. Unfortunately, sometimes lawyers get involved... But the end result should be a manual that a pilot can use to get the performance out of the machine if it is operated within the limits.
Nick, and guys like him do a great job of getting this right.